Phylum Mandibulata – Insects and Allies

It has been estimated that more than 30 million species of animals inhabit the planet currently, only about 10 million of which have been scientifically described. Phylum Mandibulata contains the largest number – there are at least 750,000 species of insects alone, leaving aside centipedes, millipedes and other unfamiliar related species. This phylum is also very ancient, having existed nearly 500 million years ago in the form of the Trilobites, the earliest animals to have eyes, which are now extinct and are thus known only from fossil remains. The first representatives of living insect families appear in the fossil record in the Devonian Period, on the order of 390 million years ago. Cockroaches appear in the fossil record as early as 200 million years ago.

All the species in this phylum have bodies with three sections (head, thorax, and abdomen) and mandibles (mouthparts) that crush food during at least one stage of their life cycle. They also all have chitin in their external skeletons. All of the species we are concerned with here are in the Class Insecta, all of which have three pairs of legs, one or two wing pairs, and one pair of antennae. Insects are the only terrestrial animals living, besides birds and mammals, that have learned to fly, primarily to avoid predators. A moment’s reflection will indicate that primarily nocturnal insect predators such as bats could not have evolved before the evolution of moths on which they prey.

There are a great many types of insects on Martha’s Vineyard, far too many for us to treat most of them here. We have chosen six groups of insects to describe in some detail because most of them will be familiar to the average reader or they are interesting for other reasons and good information is available. No island-wide, detailed survey of our insect life has been done comparable to that currently being done on Nantucket. Perhaps some enterprising young naturalist will take an interest in a group we have not discussed and conduct a thorough survey of it.  

Overview of Martha’s Vineyard Insects

By Paul Z. Goldstein, Ph.D.

Introduction

Insects and other hexapods (Phylum Arthropoda:  Class Hexapoda) comprise the most species-rich group of described organisms. They have figured prominently in seminal works in fields as diverse as behavioral and physiological ecology, evolution, biogeography, faunistics, phylogenetic systematics, speciation and conservation. Insects have figured prominently in the development of evolutionary theory and methods for elucidating phylogeneties — hypotheses of evolutionary relationships that form the cornerstone of modern systematics. Systematics and taxonomy form the cornerstone of comparative biogeographical studies which, in turn, elucidate the meaning of biodiversity. Both medically and economically, insects also figure prominently as pests and disease vectors.  

Numerous naturalists and philosophers have commented on the incredible diversity of insects. The great geneticist J.B.S. Haldane, when asked what his scientific endeavors had taught him about the nature of the Creator, supposedly replied that God had “an inordinate fondness for beetles.” Beetles are the most species-rich order, scientifically known as the Coleoptera, which means “sheath-winged,” from the Greek “coleos” and “ptera.” Although estimates of insect species richness vary between 10 and 80 million, it is clear that the vast majority of insect species are unknown to science:  Insects, with over three quarters of a million formally described species and untold numbers of recognized species known to scientists, represent centuries of intense attention by taxonomists and evolutionary biologists, and more recently by conservationists.

Discussion

Because insects are so diverse taxonomically, behaviorally, morphologically, and geographically, it is not feasible to present treatments of each and every insect group in this text. However, specific groups of known interest to the natural history of Martha’s Vineyard are treated, and references are provided for those interested in pursuing further the study of this fauna and of entomology in general. These treatments will follow a review of current invertebrate classification, an introduction to entomological studies in New England, specifically the offshore islands, and brief outlines of insect classification and collecting and observation techniques. For groups such as the beetles, butterflies, and moths that have received considerable attention from scientists on Martha’s Vineyard, some of the so-called signature groups and major families are discussed in their respective chapters following, along with case studies specific to the Island.  

New England has hosted an impressive roster of productive entomologists, including several who devoted efforts to studying the insects of Martha’s Vineyard and the other islands. Martha’s Vineyard, Nantucket, and the Elizabeth Islands have been the subject of relatively intense, but far from complete scrutiny by scientists. The first entomologists to publish treatises on the entomofauna of these areas successfully documented an amazing regional richness of insect species.  Their first major entomological publications were sponsored by the Nantucket Mariah Mitchell Association. Charles Willison Johnson published a major study of the insect fauna of Nantucket (1930). Although less than exhaustive, Dr. Johnson took on the enormous task of documenting all the insects and spiders of that island. His work stands as one of the first and best 20th century faunistic studies of the New England entomofauna.  Sadly, as lore would have it, Dr. Johnson died of a heart attack prior to his undertaking a parallel work on Martha’s Vineyard. His contemporaries, however, Dr. Charles Kimball and Dr. Frank Morton Jones, devoted decades to the study of the butterflies and moths of Nantucket and Martha’s Vineyard, respectively. Their work, which was published in 1943, has been compared to the work of Proctor on Mount Desert Island as one of the preeminent faunal works on New England insects. Important insect collections of Jones, Kimball, Johnson as well as T.W. Harris, who published the first treatment of Massachusetts insects, R.T. Thaxter and A.S. Packard, who studied the moths of New England and published numerous important and well-illustrated works, and W.M. Wheeler who studied the ants of Nantucket, reside at a variety of museums and universities throughout the country. Recent and ongoing studies by Stefan Cover, F.F. Purrington, P.Z. Goldstein, T. Simmons, and others associated with the conservation communities on Martha’s Vineyard and Nantucket have carried on this tradition, and their various collections may likewise be found at public institutions and universities.

An important generalization that can be drawn from the zoogeographical studies already completed is that the insect fauna of Martha’s Vineyard has a significant component of species which have primarily southern affinities. It is also characterized by species and groups that are hyperabundant compared to the fauna of the adjacent mainland. The Saturniid moths and the Opilionids (Harvestmen, generally known as Daddy-longlegs) represent two cases in point. 

In short, the offshore islands of southern New England, Martha’s Vineyard in particular, are especially diverse entomologically for their size and latitude.  Why are they so diverse?  It seems quite clear that the current assemblages of insects on the Vineyard are the result of a complex variety of biogeographic history and anthropogenic influences.  Biogeographically speaking, the offshore islands are remnants of an extensive coastal plain that was once contiguous and adjacent to the mainland. The ecologically diverse plant communities are functions of both ancient and recent influences by geology, weather, and man. Identifying and managing the natural areas of Martha’s Vineyard in a way that retains native faunas presents a tremendous challenge to conservationists interested in genuine biodiversity. Anthropogenic factors include the minimal history of spraying for pest insect species (a policy which will hopefully be continued); the failure of certain parasitoid species, such as certain wasps, to colonize the island though they occur on the adjacent mainland; and manipulation of the landscape to maintain areas of certain habitat types such as sandplains. 

Insect speciation

The philosophical and biological mechanics of speciation and species delineation have been a subject of debate for decades. Also, a recent renaissance of methodological and technical advances, largely associated with the advent of molecular data in the form of DNA sequence information, have precipitated renewed debates. It is well beyond the scope of this work to discuss competing species concepts and criteria. To be sure, it is unlikely that even the various contributors of this volume agree 100% on such matters as the validity of subspecies. Nevertheless, most biologists recognize that debates such as these enable vigorous scientific discussion, and for many groups of organisms may be largely irrelevant to the business of discovering and describing biodiversity. Suffice it to say that species recognition remains an important goal of professional and amateur naturalists alike, and to that end Martha’s Vineyard has presented us with unique opportunities to take advantage of a wealth of historical and current expertise.

Collection and Observation of Insects

Techniques and standards for collecting, documenting, preserving, and photographing different groups of insects are almost as diverse as the major groups of insects themselves.  Few amateur entomologists might know about the use of Styrofoam hamburger trays for pinning small moths, or the use of Pepperidge Farm pecan sandies as ant bait. In addition to baiting, other useful techniques include light trapping at night, pitfall trapping for terrestrial species, and malaise trapping. Equipment for several techniques is readily available from BioQuip or Rose Entomology, both easily located on the internet. A wealth of information awaits the synthesis of field entomological techniques in a single volume. Such a work should discuss means of collecting both aquatic and terrestrial species as well as volant ones. The standards for collecting insects vary with each group. Since the structures of arthropods vary, their requirements for preservation and photography vary also. Natural history collections are indispensable to the scientific study of all organisms, and with the development of preservation and optical techniques as well as the now routine use of molecular data in the form of DNA sequences in classification, combined with the likelihood that many of the Earth’s species will be extinct in the foreseeable future, the maintenance of natural history collections is more important than ever.  Natural history museums and university collections have undergone a renaissance in what has been termed “bioinformatics,” which can be defined as the science of maximizing information retrieval from various sources of data.  Entomologists typically document their collections through dissections, photographic images, frozen tissues, DNA extractions, and other forms of life-history information such as preserved specimens of host plants. The value of collections in the pursuit of this research cannot be overstated. These endeavors are most challenging (and expensive), but the science of entomology has always encouraged the participation of amateurs. While many collecting and preservation techniques are unpublished, a number of references do exist, and the readers of this book are encouraged to contact specialists for advice.

Comments on Specific Groups

Following are comments on three orders of insects that have been studied more or less intensively on Martha’s Vineyard. These three groups are the best inventoried, though there is much more to learn, especially for the beetles.

Dragonflies and Damselflies: Order Odonata

These fascinating creatures are among the earliest and most charismatic winged insects. Behaviorally, adult odonates have proven incredibly important to studies of mating behavior and ecology. The odonates are also one of the groups to which anybody with some rudimentary collecting equipment can make a real contribution, primarily because regional faunas, even in New England, need a great deal of further study. Collection techniques of adult dragonflies and damselflies have been advanced to preserve the colors and fragile structures. Nymphal odonates, known as naiads, are also in need of collection-based research, and numerous efforts are underway to develop collections around the world. Odonate naiads are fascinating creatures in being among the only insects that regularly feed on vertebrate prey, including small fish and tadpoles. They are also outstanding indicators of water quality and have enjoyed a growing role in invertebrate conservation efforts.

Like butterflies and tiger beetles, adult odonates have become incredibly popular with photographers and bird-watchers. Although many small species are not reliably determined by sight, the observation of these animals is one of the best ways to introduce naturalists and children to the study of entomology.

Moths and Butterflies: Order Lepidoptera

The Lepidoptera comprise one of the most diverse and charismatic orders of insects, with roughly 150,000 described species and an estimated 200,000 awaiting discovery.  Lepidoptera are considered the second most diverse order of insects, following the beetles (Coleoptera). The moths and butterflies have featured prominently in entomological studies on Martha’s Vineyard as well as throughout southern New England (Massachusetts Natural Heritage and Endangered Species Program website; Grand and Mello 2004). This is the best-studied insect group in this region thanks to a steady history of New England-based entomologists, both amateur and professional.

Because of their beauty, often requiring a microscope to see, and their diversity, Lepidoptera are popular with amateur naturalists and photographers as well as professional entomologists. Along with dragonflies and damselflies, their collection and documentation by amateurs continues to make valuable contributions to basic science, and many students of entomology get their start by collecting and observing these fascinating creatures.  Lepidoptera have figured, perhaps more widely than any other order, in the development of numerous biological fields (e.g. the development and evolution of wing patterns, the elucidation of metamorphosis, plant-insect interactions) and phenomenological sub-disciplines (e.g. mimicry, co-evolution, migration, and the evolution of flight).

While butterflies enjoy the greatest popularity of any insect group and have become the focus of the sprouting butterfly-watching movement, their taxonomic diversity is just one piece of a greater lepidopteran puzzle taxonomically.  Butterflies and skippers represent remarkable species radiations, and have sat at the nexus of important evolutionary studies surrounding mimicry, co-evolution, and biogeography. Yet they represent a minority of taxonomic diversity within the Lepidoptera. Butterflies and their relatives, the skippers, make up two of the roughly 46 superfamilies of Lepidoptera, the latter of which comprise some 127 recognized families as of this writing, including newly described and newly resurrected groupings. It is conceivable that the butterflies will one day fall within one of the moth superfamilies, but this hypothesis will await considerable testing through morphological and molecular data. In a way, butterflies and skippers are simply moths that have become day-fliers, and although they can be readily distinguished, they are in fact an evolutionary sub-group nested within the greater order.  Perhaps the first question asked by those curious about the taxonomy of Lepidoptera is “What is the difference between a moth and a butterfly?” The answer requires an understanding of the evolutionary history of Lepidoptera, in that butterflies and skippers represent relatively recently evolved groups that can be represented diagrammatically as nested within moths, much like rabbits are nested within mammals.

Another important distinction, that between the informally classified microlepidoptera and macrolepidoptera, warrants explanation. Roughly half the species recorded from Martha’s Vineyard and Nantucket are very small and comprise the older superfamilies of the Lepidoptera. But the terms “microlepidoptera” and “macrolepidoptera” are compromised because many so-called microlepidopteran groups contain rather large species; likewise many macrolepidopteran groups include atypically small species. Larger moths and butterflies are, to be sure, most easily studied because their observation and preparation are more easily undertaken than the tinier animals whose adults and larvae require more specialized training and expertise.

Although a number of Lepidopteran species have been introduced, intentionally or accidentally since human colonization, several populations highlight the deeper history of these areas. The moths and butterflies provide some excellent examples. The geometrid or inchworm species called the Woolly Gray, Lycia ypsilon, occurs nowhere else in New England. Yet it is clearly a biogeographic remnant and not an introduction, for the obvious reason that females of this species are flightless. This is a barrens species whose caterpillars feed on Scrub Oak Quercus ilicifolia (Wagner, 1997). Its nearest occurrences are in pitch pine scrub oak barrens on Long Island and in southern New Jersey.

The butterfly fauna of New England, while not especially diverse, nonetheless includes a number of regionally rare or threatened species as well as species that have disappeared within our lifetimes. These include the famous Regal Fritillary Speyeria idalia, arguably North America’s most stunning butterfly and a poster child for invertebrate conservation. This beautiful animal made its last stand in New England on five of the offshore islands (Martha’s Vineyard, Nantucket, Block Island, Naushon Island, and Nomans Land Island) before disappearing from the region in 1992. This animal epitomized many of the conservation concerns on Martha’s Vineyard, particularly the health of the sandplain region.

Beetles: Order Coleoptera

The beetles comprise the most diverse group of insects, with an estimated 500,000 described species and countless as-yet unknown to science.  Like most primarily herbivorous insect groups, the more than 200 families of beetles have evolved and diversified in concert with the origins of flowering plants. Some beetle families are so diverse that local inventories are problematic because taxonomic experts are so rare. In the Martha’s Vineyard/Cape Cod/Islands region, our understanding of the beetle fauna is perhaps better than in some other New England areas; however, a great deal more work is needed. A select few groups of beetles have received attention by entomologists in this area:  Following Johnston’s (1934) inventory of Nantucket insects, Purrington (1996) revisited the ground beetle fauna of that island, Goldstein and Simmons (2003) treated the scarab beetle fauna of all the offshore islands, and ongoing projects devoted to tiger beetles (a subfamily of ground beetles) and longhorn beetles (Family Cerambycidae) continue.

Tiger beetles are often considered the “butterflies” of the beetle world:  their beauty and diversity have garnered impressive attention from collectors and professional entomologists, and as a result their distributions and diversity have been the subject of numerous recent studies and books—including several devoted to the New England and Martha’s Vineyard faunas. Tiger beetles have scientifically enjoyed their own journal — Cicindela — which has been successfully in press since 1980. Although tiger beetles are often accorded family status (Cicindelidae), they are in fact a particularly diverse subfamily of the ground beetle family Carabidae. Tiger beetles, which are found nearly all over the world, occupy a wide variety of habitats. They are so named because of the voracious habits of their larvae, which are ambush predators that reside in subterranean tubes and trap passing invertebrates, and of their adults, which are incredibly fast-moving cursorial predators.

Ants: Order Hymenoptera

The large Order Hymenoptera includes the wood wasps, sawflies, ichneumon flies, chalcid wasps, bumble bees and honey bees in addition to the ants. The ant species of Martha’s Vineyard are under current study by S. Cover and P. Z. Goldstein and a paper is planned for a scientific journal which will discuss the species present and their zoogeographical affinities and origins in detail. A partial list of the known species appears in its own chapter elsewhere in this work. 

There are two orders that have been little studied on Martha’s Vineyard where an investment of time and effort would reap significant rewards. One is the Diptera and the other is the order Hymenoptera, a group which includes the ants as mentioned above. 

Flies: Order Diptera

 The great German systematist Willi Hennig, who was the first to articulate phylogenetic theory, was a Dipterist: he studied flies, one of the most diverse orders of insects. His contemporary Lars Brundin, another dipterist, was the first to apply phylogenetic theory to the study of historical biogeography. There are at least four suborders and such species as crane flies, midges, mosquitoes, robber flies, and various species which are parasitic either as adults or as larvae.

Bees and Wasps: Order Hymenoptera

 This large order contains some of the most specialized insects living, many of which have developed sophisticated social lives or highly evolved forms of parasitism on other insect species. There are two suborders, and representatives of both are known to occur on the island. Many species are beneficial, particularly honey bees and other bees, for their services as pollinators of flowers, without which many plants could not exist. It is hoped that studies of the species that pollinate rare plants on the island can be initiated in the near future. 

Conservation

Given the richness of formally threatened species on the island (on the order of 30), land management and conservation professionals, municipal planning boards and conservation commissions should be especially vigilant to prevent harm to populations at risk. Specialists should be consulted if there is any question about the presence or status of species listed by the Massachusetts Natural Heritage Program on a property proposed for development. 

Directions for future regional faunistic studies

 Insect faunas are extremely dynamic and diverse, and a lack of available expertise is generally the greatest obstacle to full-blown faunistic studies. I would estimate that a full-time “A-team” of five entomologists that included experts in the major groups could inventory 75% of the island’s insect fauna (both terrestrial and aquatic species) provided adequate resources, a technical team for pre-processing specimens between May and September, and the willingness of at least 20 experts on the more obscure groups to provide determinations, with the recognition that numerous species awaiting formal description will likely remain nameless for years. It would be the hope that such a broad investigation of the island’s insect fauna would also shed light on some of the ongoing controversies in entomology such as phylogenetic relationships, taxonomy, systematics and collecting policy and techniques. 

Paul Goldstein and Allan Keith; edited by Matt Pelikan, July 18, 2022