Insects and Their Relatives

By Bugboy52.40 (Derivative from images uploaded by Fir0002.) [CC BY-SA 3.0 ( or GFDL (], via Wikimedia Commons

Insects make up over 60% of organisms on earth. Our very existence is dependent upon them. Each insect has its own ecology, and impacts upon many other species.

What are the major roles of insects?  About 40% are plant eaters, the rest are meat eaters and those which eat things which are decaying.  They are major players in food-webs.  They regulate populations of other organisms by hunting, living as parasites, cross-pollination, and by carrying diseases.

What is the basic structure and function of the parts of an insectInsects have a shell-like exoskeleton that helps protect them from drying and injury, plus provides places for their muscles to attach so that they can move or gain leverage. This allows them to make leaps that would be like humans being able to jump the length of three football fields! 

The body of an insect is composed of three parts.  The head houses the central headquarters of their nervous system, sight, some hearing, and mouth parts.  The thorax is the center, where legs and wings attach to the body.  The abdomen houses the digestive and reproductive tracts and is the main energy storage area for fat.

Insects undergo metamorphosis, changing form as they develop and age.  All insects start out as eggs, then molt (usually five times) as they become increasingly larger, moving from immature stages such as larvae, nymphs or naiads into pupae (in higher forms) and finally to 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 some species die soon after reproducing.

The four major types of metamorphosis are: 

  1. Simple metamorphosis, where the immature stages 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 nymph.
  3. Incomplete metamorphosis where the immature insect 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.
  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 are at the top of the list.  All are various modifications of palps (helper appendages near the mouth) and upper and lower jaws. 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 abound in insects.  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. In addition, compound eyes see images and the small, simple eyes record direction and duration of light, plus control of some hormonal activity. Most insects are near-sighted.  The antennae in some moths are more sensitive to tiny concentrations of smells than some of the best lab equipment.
 4)  Structures and nerve endings at the back end of insects 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!

Insect Relatives:

Other than insects, the Arthropods  make up five other common classes of organisms we associate with insects.   As we look at those five, only the ones typically found Dungeness River habitats will be discussed.


Sowbugs & pillbugs.  They have 5 pairs of legs and 2 pairs of antennae-like projections.  They look like old VW cars.  They are harmless (unless you’re a strawberry) and good scavengers. 


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.  All are predators.


Millipedes have more legs than centipedes, with two pairs of legs per body segment.  They do not bite or harm you.  Our local black and yellow Clown Millipede smells of almond or garlic when handled because it releases a cyanide compound. Millipedes in our area are scavenger and feed on decaying plant material.


All have 4 pairs of segmented legs and have only 2 body regions; one is called the cephalothorax which is a fusion of the head and chest, the other is the abdomen. They may have “fangs” or “pinchers,” but never have antennae.  The Arachnid class has six orders in North America, but only three orders of interest in the Sequim region:

1) Spiders – These 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” – These 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. 

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.  Mites prefer plant and animal fluids; and can be predators, parasites, or scavengers.  Ticks have widespread legs and feed only on the blood of vertebrates.  Some may only feed once a year! Ticks can be vectors of serious diseases.

The Big Four Insect Orders
in Railroad Bridge Park
Beetles & Weevils | Bees, Wasps, Ants & Sawflies
True Flies | 
Butterflies, Moths and Skippers

Beetles & Weevils

Beetles & Weevils  (Coleoptera “coleos” = sheath, “optera” = wing):
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 characteristic of beetles.  All beetles have chewing mouth parts and undergo complete metamorphosis.  Beetle types are very diverse, including plant feeders, predators, scavengers, and some that only live in termite and ant colonies.

1) Predaceous ground beetle (Carabidae) – Lively, mostly nocturnal, “eating machines,” tigers of the insect world.   They may be easily confused with the slow moving darkling beetle or “iron-clads.”

2) Ladybird beetles, or ladybugs (Coccinellidae) –  All are predaceous in this area.  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 chest that give them the ability to click.

5) Scarab beetle (Scarabaeidae) — “C” shape larvae (white grubs).  Adults have “lamellate” antennae which look like a club with little side-by-side fingers.  This variety includes “June bugs”

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 on it (not arising on the head, as with other beetles).  There are over 60K species of weevils in the world.

Bees, Wasps, Ants & Sawflies

Bees, Wasps, Ants, and Sawflies (Hymenoptera “membrane” wing):
The sawflies, bees, wasps and ants have chewing or lapping mouth parts and undergo complete metamorphosis.  All members of this group have two pairs of wings which are joined together with tiny hooks (hamuli) as they fly.  They may be confused with flies, which have only one pair of wings.

1) Sawflies and horntails – These are a large group of “broad-waisted” wasps where the thorax and abdomen seem like one piece in adults.  The larvae look and feed like caterpillars.

2) Wasps – Includes many social and solitary kinds.  Wasps are meat eaters (adult & larvae) and have simple body hairs.  Examples are “mud-daubers”, “paper-wasps,” “yellow jackets,” “velvet ants,” and parasitic wasps.

3) Bees – All bees have hairs which look “fuzzy” because of tiny side branches that hold pollen, the source of protein for their young.  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.  Thank honey bees for cross pollinating over 90% of the crops we eat! 

4) Ants  – All ants have “elbowed antennae” and a narrow constriction between the thorax and abdomen called a pediole.  There are 2500+ species of ants and all have well-developed social lives.  Our largest ant, the carpenter ant,  mine wood for their tunnels and nests, not for food. 

True Flies

True Flies (Diptera “two wings”):

The flies, another huge group of higher insects, are identified by having only one pair of wings. Flies are extremely important in the food chain, which is often overlooked when we think of them as medical and agricultural problems.

True Flies commonly found at Railroad Bridge Park:

1) Crane flies –  Their larvae live in moist areas.  Adults look like flying daddy-long-legs, or giant mosquitoes (can also be confused with scorpionflies).  Adults do not eat, instead living off of fat left over from their larval stage.  They are short lived as adults.

2) Mosquitoes – They have aquatic larvae.  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 – Midges look like mosquitoes, but without stylets or hairs on veins.  They have very fuzzy antennae.  None suck blood.  They are important for the food-chain; in the Arctic, their larvae are an important food for nesting shorebirds.

4) Horse & Deer flies  – Biting flies with large “rainbow” colored eyes.

5) Robber flies 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  –  Yes, they often hover as they feed on flower nectar and pollen.

7) Muscoid flies – Includes several dozen families that look like and include house flies.  Also includes stable, blow, bluebottle, flesh and parasitic flies.  The parasitic flies have stiff hairs on the upper side of their abdomens.

Butterflies, Moths and Skippers

Butterflies, Moths and Skippers (Order Lepidoptera “lepido” = scale, wing)

This is 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 immature forms to a coiled tube, the proboscis,  in the adult.  Adults have 2 pairs of wings that function as one, joined by tabs & hooks.  Butterflies have scales on their wings, while moths have hairs.  T

Lepidoptera commonly found at Railroad Bridge Park:

1) Swallowtails – The larvae are found on plants in the carrot family, and  have a forked orange gland that pops out behind the head at will or when you poke it.  Adults are generally large yellow and black butterflies with “tails” on their hind wings, which gives them their common name.

2) Whites & Sulphurs  – Includes European Cabbage White,butterfly, a bad pest for cabbage and related plants. Its was introduced accidentally near Montreal, Canada in the 1860s.  The larvae are bright green.

3) Blues, coppers & hairstreaks –  Small butterflies.  Their names describe their colors.

4) Four-footed butterflies –  Checkerspots, ladies, buckeyes, admirals, viceroys.  They have only 2 pair of legs as adults (the hind pair are very reduced).   All are medium-sized, often with orange markings. Larvae usually bear branching spines on their tops and sides.  They are found on willows.

5) Skippers –  Robust little guys, with antennae which are hooked at the ends.  When their wings are at rest the front wings are vertical and the hind horizonal.

6) Inch worms are the larval name of many moths that lack prolegs in their immature form.  They have only one pair and a anal pair, hence the undulating locomotion.

Four Dungeness habitats in which to find insects:

Under soil beneath trees

The top layer 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 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 

Small insects in these habitats are camouflaged, 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 predatory ground beetles scurry about.

Under rocks in 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. 

Note – This just touches on the many insects you could see in Railroad Bridge Park.  Strike out on your own to identify the other, equally fascinating, insects in the park!