INSECTS AND THEIR RELATIVES
by Ron Stecker, Ph. D., Professor Emeritus of Entomology, San Jose State University
Insects alone make up over 60% of the 1.85+ million described species of organisms on earth. Our very existence is dependent upon them. Each insect has its own ecology, with impacts upon many other species. They are thought to have evolved more that 400 million years ago, long before land plants and dinosaurs!
What are the major roles of insects? About 40% are phytophagus (plant eaters), the rest carnivorous (meat eaters) and saprophagus (eat decaying matter). They are major players in food-webs, usually occupying second and third trophic levels. They regulate populations of other organisms by predation, parasitism, cross-pollination, and by vectoring diseases.
What is the basic structure and function of the parts of an insect? They are housed in an exoskeleton that helps protect them from drying and injury, plus provides muscle attachments for movement and leverage. This allows leaps that would equate to humans being able to jump the length of three football fields! The body is always composed of three parts: head, thorax, and abdomen. The head houses neural headquarters, sight, some hearing, and mouth parts. The thorax is the locomotor center, with three pairs of segmented legs and one or two pair of wings (some wingless). The abdomen houses the digestive and reproductive tract and is the main energy storage area of fatbodies.
Insects undergo metamorphosis, changing form as they develop and age. All insects start out as eggs, then molt (usually five times) as increasingly larger immatures (larvae, nymphs, naiads) into pupae (in higher forms) and finally adults. The egg and pupal stages are usually “resting” stages that can overcome adverse times of year (cold, heat, lack of food). The immature stages are the growth or “teenage years”. The adult stage is mainly reproductive and in some is dispersal. The four major types of metamorphosis are: 1) “Simple metamorphosis”, where the immatures look like small versions of the adults and are wingless, as in silverfish. 2) “Gradual metamorphosis”, such as grasshoppers and aphids, where the wing pads develop externally on each immature (nymph). 3) “Incomplete metamorphosis”, where the immature is aquatic and is called a “naiad” and also has externally developing wing pads. This applies to three groups: mayflies, stoneflies, and dragonflies and damselflies (note each is one word, only Diptera as true flies are two words). 4) “Complete metamorphosis”, where a fourth stage of development is present, egg – larva – pupa – adult. The wing pads develop internally in this group, such as beetles, bees, flies and butterflies.
What are the most important modifications in insects?
1) Several different kinds of mouthparts head the list. All are various modifications of palps, mandibles, and maxillae. They can be chewing (grasshoppers), sucking (aphids), siphoning (butterflies), or lapping (bees) in function. Look at an insects’ mouthparts with a hand lens to see how complex the paired parts are.
2) Modification of legs can help the insect to adapt: i.e., grasping legs (mantids), running legs (cockroaches), jumping legs (grasshopper), and swimming legs (water beetles).
3) Sense organs and apparati abound in insects. The legs and mouthparts mentioned above are loaded with sensory nerve endings. The compound eyes (28,000 facets in dragonfly eyes) see images and the small simple eyes (three ocelli) record direction and duration of light, plus control of some hormonal activity. Most insects are near-sighted. The antennae in some moths, which may have thousands of chemoreceptors, are more sensitive to tiny concentrations of smells (parts per billion) than some of the best lab equipment. The entire bodies of insects are often covered with tiny hairs and small pits that help to monitor the environment for sounds, smells, and touch.
4) Structures and nerve endings at the back end of insects (such as cerci, which look like stubby antennae) monitor the blind spot of an insect. The ovipositor lays eggs and may serve as a stinger in others. Some wasps can lay eggs as deep as three inches into solid wood!
Other than insects, the Phylum Arthropoda comprises five other common classes. For each, only the organisms typically found in habitats of the lower Dungeness River will be discussed.
Crustaceans – sowbugs & pillbugs. They have 5 pairs of segmented legs and 2 pairs of antennae-like projections. They look like old VW sedans. They are harmless (unless you’re a strawberry) and good scavengers. (This group also includes many marine arthropods, including crabs, shrimps, and others)
Centipedes – These have at least 9+ pairs of walking legs, with only one pair of legs per visible body segment. They have a pair of poison-injecting “jaws” (modified legs) behind their head. They are safe to handle in Washington, but not in Hawaii (worst pain I have ever had – they treat the “bite” with Novocane!). All are predators.
Millipedes – Millipedes have more legs than centipedes (except some in the tropics), with two pairs of legs per body segment (really every two segments fuse when the animals are young). They do not bite or harm you. Some release a dark fluid; our local black and yellow Clown Millipede (Harpaphe haydeniana) smells of almond or garlic when handled because it releases a cyanide compound. Our millipedes are scavengers on decaying plant material.
Arachnids – All have 4 pairs segmented legs and only 2 body regions (a cephalothorax and abdomen). They may have “fangs” or “pinchers”, but never have antennae. The class Arachnida has six orders in North America, but only three orders of interest in the Sequim region, as follows:
1) Spiders – Have poison “fangs.” All are predators (very beneficial). The connection between their abdomen and head is narrowly stalked and their legs are less than 7 times the length of body.
2) Harvestmen or “Daddy Long-legs” – Have tiny “pinchers” (no fangs) and their abdomen is not stalked. They are harmless to humans, but they are predators on mites and other small arthropods. Their abdomen shows segmentation and their legs are more than 7 times as long as body. They are very slender, looking like crane flies to some people.
3) Mites & ticks – Have no poison fangs or “pinchers” and their abdomen is not segmented or stalked. Their first larval stage has 6 legs, then 8 legs in later stages. Mites are very SMALL (under 2mm), and ticks are slightly larger (2 to 10mm). Mites prefer plant and animal fluids; some are predators, parasites, or scavengers. Ticks have widespread legs and feed only on the blood of vertebrates. Some may only feed once a year! They can be vector of serious diseases.
Four selected Dungeness area habitats to find insects:
Under canopy soils – The duff or litter composed of whole and decaying leaves offers a rich habitat for small insects and insect relatives. Examine this material closely by spreading it on a sheet and turning it back and forth. The top soil beneath harbors insects even harder to find, but still very important.
Attached to leaves - Sweep with a net from the undersides of leaves to check for insects in trees. In open sun, stop and observe, seeing how many insects (and their feeding damage or waste) you can see before sweeping with net. Check flower heads. Willows are good host plants for aphids, leaf hoppers, scale insects, galls, flies, and wasps.
Gravel and sand bars – The problems here for insects includes visual hunters (Bob’s birds & some insects), solar heating, and desiccation. Small insects in these habitats are camoflaged, often color-coded to the substrate, with large eyes. Many are nocturnal. Look under larger rocks and chunks of wood (Replace these! It’s their home!). Near the stream, splash water on the bank and watch predaceous ground beetles scurry about.
Under rocks in the the river and side channels - Several types of insects specialize in freshwater habitats, such as stoneflies, mayflies, and caddisflies. They may be predators, scavengers, or algae scrapers. Carefully look under rocks in the river and side channels for these. (Also see Victor McAllister’s description of aquatic insects following this account)
Order Coleoptera (“coleos” = sheath, “optera” = wing): Beetles & Weevils
The beetles and weevils make up one-fifth of all species of animals known in the world and comprise about 40% of all insects. Their front wings, called “elytra” are thick and hardened and are not used in flight, but open like barn doors to allow the rear wings to emerge. Elytra are the key ID characteristic for beetles. All beetles have chewing mouth parts and complete metamorphosis. Beetle biology is exceedingly diverse, including plant feeders, predators, scavengers, and some that only live in termite and ant colonies (termitophiles, myrmecophiles).
Beetles commonly found at Railroad Bridge Park:
1) Predaceous ground beetle (Carabidae) – Lively, mostly nocturnal, terrestrial “eating machines”, tigers of the insect world. All have a tarsal formula of 555 (segments of feet, front to rear). They may be easily confused with the slow moving darkling beetle or “iron-clads”, a scavenger with a tarsal formula of 554.
2) Ladybird beetles, or ladybugs (Coccinellidae) - All are predaceous in this area. Tarsal formula of 333 (apparent). May over-winter in clusters. They are good bio-control agents for aphids!
3) Rove beetle (Staphylinidae) – These are elongated with very stubby elytra (like wings of earwigs). Both larvae and adults are predaceous. Some live in ant and termite nests.
4) Click beetle (Elateridae) – Also elongate; can flip or jump when upside down. Note the spine and pit underside of thorax that make up the clicking mechanism.
5) Scarab beetle (Scarabaeidae) – “C” shape larvae (white grubs). Adults have “lamellate” antennae (a club with little side-by-side fingers). Show great diversity of habits. Includes “June Bug.”
6) Leaf beetle (Chrysomelidae) – a diverse plant-eating group. Look like elongated ladybird beetles (elm leaf beetle, cucumber beetle)
7) Weevils (Curculionidae) – These beetles have a snout or beak, with elbowed antennae arising on it (not arising on the head, as other beetles). May drill hole in a seed, turn around and lay an egg. Offspring can mature in the one seed! There are over 60K species of weevils in the world.
Order Hymenoptera (= “membrane” wing): Bees, Wasps, Ants, and Sawflies
The sawflies, bees, wasps and ants have chewing or lapping mouth parts and have complete metamorphosis. All members of this group have two pairs of wings (some wingless) with tiny hooks (“hamuli”) along the front edge of the rear wing that holds the wings together as one airfoil. They may be confused with flies, which have only one pair of wings.
Hymenoptera commonly found at Railroad Bridge Park:
1) Sawflies and horntails (several families) - These are a large group of “broadwaisted” wasps (lack a pediole) where the thorax and abdomen seem like one piece in adults. The larvae look and feed like caterpillars. They have more than five pairs of prolegs (see discussion under Lepidoptera).
2) Wasps (several families) - Includes many social and solitary kinds. Wasps are meat eaters (adult & larval). The body hairs are never plumose. Example are “mud-daubers”, “paperwasps”, “yellowjackets”, “velvet ants”, and parasitic wasps (a huge group of bio-control fame that keeps some other insect populations in check)
3) Bees (several families) - All bees have plumose hairs, i.e. the hairs look “fuzzy” because of tiny side branches that hold pollen, their source of protein for young (wasps, above, provide meat to their young, and have simple hairs). Examples of bees in our area are honey bees, bumble bees and carpenter bees. The latter look like bumble bees, but lack color bands on their abdomens. They mine old wood for nest sites. Thankhoney bees for cross pollinating over 90% of the crops we eat! All the books about their social behavior would fill a semi truck!
4) Ants (Formicidae) – All ants have “elbowed antennae” and have a trailer tongue affair that constricts between the thorax and abdomen = pediolate condition. The 2500+ species of ants have well-developed social lives. Our largest ant, the carpenter ant, has a convex top side to its thorax (good for I.D.). They mine wood for their cavities and nests, not for food. You name it - ants do it! All the ants in the world outweigh all of us primates and maybe the rest of the other mammals put together.
Order Diptera (= “two wings”): True Flies.
The flies, another huge group of higher insects, are identified by having only one pair of wings. The hindwings are modified (halteres) into organs of equilibrium, “gyroscopes,” if you will, that look like little stick shift knobs. Flies are extremely important in the food chain, which is often overlooked when we think of them as medical and agricultural problems, carriers of malaria, yellow fever, encephalitis, sleeping sickness, dengue and so on!
Diptera commonly found at Railroad Bridge Park:
1) Crane flies (Tipulidae) - Their larvae live in moist areas. Adults look like flying daddy long- legs, or giant mosquitoes (can also be confused with Mecoptera, or scorpionflies). Adults do not eat, instead living off of fatbodies from their larval stage, and hence are short lived as adults.
2) Mosquitoes (Culicidae) - They have aquatic larvae. Terrestrial adults identified by veins of wings having tiny hairs (need at least 10X mag.), and mouth parts elongated into thin stylets. Males generally feed on plant juices. Only females take blood; they must have a blood meal before producing eggs. They, of course, are vectors of many human diseases.
3) Midges (Chironomidae and several other families) – Midges look like mosquitoes, but without stylets or hairs on veins. They have very plumose (fuzzy) antennae. None suck blood. Big time food-chain organisms! In the Arctic, their larvae are an important food for nesting shorebirds.
4) Horse & Deer flies (Tabanidae) – Biting flies with large “rainbow” colored eyes.
5) Robber flies (Asilidae) have a long tapering abdomen and a notch on top of the head between the eyes. They often sit in ambush of flying insects on the uppermost ends of limbs of down trees.
6) Hover or Flower flies (Syrphiidae) - Yes, they often hover. All have a spurious vein in the wing.
7) Muscoid flies – Includes several dozen families that look like and include house flies. Also includes stable, blow, bluebottle, flesh and parasitic flies. The latter, tachinids, have stiff hairs on the dorsum of their abdomens and are endoparasites of caterpillars.
Order Lepidoptera (“lepido” = scale, wing): Butterflies, Moths and Skippers
The classic group used to illustrate metamorphosis from egg, caterpillar, pupa, and, like a whole new organism, the adult butterfly. They have gone from chewing mouthparts in immatures to a coiled tube, the proboscis, (best I.D.) in the adult. Adults have 2 pairs of wings that function as one airfoil (tabs & hooks). Butterflies have scales on wings, while moths have hairs. The larvae have a head capsule, a thorax with three pairs of segmented walking legs, an abdomen with four “prolegs,” and one pair of anal legs. The prolegs have tiny rows of hooks (“crochets”) at their ends that help the larva hang on to leaves. Each family of leps have different configurations of crochets, used for accurate I.D.
Lepidoptera commonly found at Railroad Bridge Park:
1) Swallowtails (Papilionidae) – The larvae are found on umbelliferous (carrot family) plants, and have a forked orange gland that pops out behind the head at will or when you poke it. Be sure to smell it! Adults are generally large yellow and black butterflies with “tails” on their hind wings, hence the common name.
2) Whites & Sulphurs (Pieridae) - Includes European Cabbage White, a bad pest for cruciferous plants, which was introduced accidentally near Montreal, Canada in the 1860s. The larvae are bright green.
3) Blues, coppers & hairstreaks (Lycaenidae) - Small butterflies. Their names tell their colors.
4) Four-footed butterflies (Nymphalidae) - Checkerspots, ladies, buckeyes, admirals, viceroys. They have only 2 pair of legs as adults (hind pair very reduced). All are medium-sized, often with orange markings. Larvae usually bear branching spines on their tops and sides. Found on willows.
5) Skippers (Hesperiidae) - Robust little guys, with antennae hooked at ends. Wings at rest are held with the front wing vertical and the hind horizonal.
6) Inch worms (Geometridae) - the larval name of many moths that lack prolegs as immatures. They have only one pair and a anal pair, hence the undulating locomotion.
Note – This just touches on the many insects you could see in Railroad Bridge Park. We have omitted 20 other orders of insects, some very important such as the Hemiptera and Orthoptera. You must strike out on your own to identify the other, equally fascinating, insects in the park.