UC Davis Natural Reserve System
Stebbins Cold Canyon Reserve
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Insects of Cold
Canyon
Also, because insects are so incredibly diverse, even taxonomic experts at the University of California, Davis, have only been able to catalog completely the insect orders and families of the reserve. The following descriptions are grouped by insect orders, and some descriptions of particular families, genera, or species are also included. The taxonomy used in this web site comes primarily from An Introduction to the Study of Insects (D. J. Borror, C. A. Triplehorn, and N. F. Johnson, 1989, 6th edition, Saunders College Publishing, Philadelphia). The evolutionary relationships of many insects are still under debate, so beware that the taxonomy in your insect field guide may vary somewhat from that used below.
An excellent resource for the interested entomologist is California Insects (J.A. Powell and C.L. Hogue, 1979, University of California Press, Berkeley), which provides descriptions and illustrations of most of the insect species mentioned as well as additional ones not covered in this web site.
Aquatic and semi-aquatic insects
A day of aquatic entomology in Cold Creek will reveal insects on the surface of the water, in open water, in the debris on the bottom, and attached to submerged rocks. For a more complete list of insects, look at the Insect Families Checklist.
True bugs (Order Hemiptera). The surface tension of the still waters of Cold Creek supports an amazing diversity of life. Numerous insects glide, buzz, and whirl in an aesthetically pleasing but seemingly purposeless dance. In actuality these highly adapted insects are actively hunting or courting as they swirl across the surface. The most common semi-aquatic insect of the reserve is the water strider (Gerris remigis: Gerridae), which preys on unfortunate terrestrial insects that fall into the water. Water striders are clearly visible on slow water because of their long middle and hind legs; however, look closely and you will also notice their short front legs, used to capture prey.
Another insect in this order, the toad bug (Gelastocoris sp.: Gelastocoridae), earns its name. Roughly the shape and size of a small toad, it hops along the shore, leaping on top of its insect prey. If threatened, the toad bug jumps into the stream and swims to safety.
There are also several conspicuous, truly aquatic members of this order in the waters of Cold Creek, including water boatmen, backswimmers, and giant water bugs. Most of these bugs spend their lives swimming in open water or clinging to submerged vegetation, rising to the surface only for air. Water boatmen (Graptocorixa californica and Sigara mckinstryi: Corixidae) have elongated oval bodies and oar-like hind legs. Backswimmers (Notonecta undulata Notonectidae) look quite similar, but, as the name implies, swim on their backs. Also, water boatmen eat algae and do not bite humans, whereas backswimmers are predatious and will give you a bite like a bee sting if you give them the opportunity. The giant water bugs of Cold Creek, amusingly named toe biters (Abedus indentatus: Belostomatidae), are indeed capable of inflicting a long-lasting bite. They look like very large, broad water boatmen. However, unlike water boatmen, they frequently fly out of the water and do not have oar-like hind legs. Female toe biters lay their eggs on the backs of the males, so if you see an egg-clad bug by the creek, it is probably a giant water bug.
Beetles (Order Coleoptera). The largest order in the animal kingdom, the beetles are too diverse to cover in any depth, but look for their characteristic oval body shape with non-overlapping elytra, or hard wing covers, covering most of their backs.
Swarms of whirligig beetles (Gyrinus plicifer: Gyrinidae) can be found either on or below the surface of the quiet areas of the creek, usually twirling madly about en masse. The beetles have two pairs of compound eyes that enable them to watch for prey above and below the water simultaneously. To avoid collisions, the beetles rest their antennae on the water and can sense the presence of another object by the tilt on the water’s surface.
Mayflies (Order Ephemeroptera). Although inconspicuous, invertebrates living on the stream bottom under rocks, sand, and submerged leaves - especially in riffles - are in fact the most numerous. In this hidden world, nymphs, or juvenile forms of insects, feed and grow. Some filter feed, others wait surreptitiously for prey. Mayflies (Baetis sp.: Baetidae, and Ameletus sp.: Siphlonuridae) are abundant, and, as herbivores, serve as an important source of food for both vertebrate and invertebrate aquatic predators. Although the juveniles spend months under the debris of the creek, the winged adult forms spend only hours flying around in a mating dance above the creek. If you see a mating swarm, enjoy the sight for the ephemeral delight it is.
Stoneflies (Order Plecoptera). Stonefly nymphs (Kogotus alameda:) can be found in the bottom of the creek alongside mayfly nymphs. Although both groups look quite similar, they can be differentiated on the basis of tail number: stonefly nymphs have two while mayfly nymphs almost always have three.
Flies (Order Diptera). Black fly larvae (Prosimulium sp.: Simuliidae and Simulium sp.: Simuliidae) can be found in abundance in Cold Creek. Club-shaped black fly larvae form dense black mats on many rocks in the creek. Although you will have to seek out the larvae in order to see them, the adults will be glad to come to you. Adult females are predatious on blood and give a nasty bite. Female deer and horse flies (Chrysops sp.: Tabanidae and Tabanus sp.: Tabanidae) do the same but can be differentiated from black flies because they are smaller and tend to be brownish.
Terrestrial insects are virtually everywhere as you hike in the reserve. Look for them in the leaf litter, on tree trunks and leaves, at flowers, and flying through the air. Once you begin noticing insects, you will find that they are everywhere.
Although enormous effort has been invested in the study of the evolutionary relationships of insects, a precise phylogeny, or evolutionary tree, has yet to be completed. The following list of orders reflects the current understanding of insect phylogenetic relationships, with the most ancestral orders appearing first.
Silverfish (Order Thysanura). To find silverfish, you need only dig through leaf litter or a decaying log, where they feed on decaying plant material. The most common silverfish in the reserve is the spined silverfish (Allacrotelsa: Lepismatidae), a long, brown, scaly creature with prominent antennae and three tails.
Dragonflies and damselflies (Order Odonata). These conspicuous and often beautiful insects congregate in clearings adjacent to the main trail, where swarms of gnats and other small flies provide the dragonflies and damselflies with ample food.
Though the nymphs of this group are aquatic and cryptic, the adults are easy to spot. The common green darner (Anax junius: Aeshnidae) is a large bright green dragonfly with yellowish, transparent wings which buzzes around the ponds that form in the upper creek. A related dragonfly (Aeshna multicolor: Aeshnidae) sports two yellow diagonal markings on its dark thorax. Both are spectacular to watch as they perform their courtship and territorial acrobatics. Also enjoy the plethora of blue damselflies (Coenagrionidae), which look like small, delicate dragonflies.
Crickets and grasshoppers (Order Orthoptera). One only needs to lift a small boulder or fallen log to observe a myriad of insect life. Jerusalem crickets (Stenopelmatus fuscus: Stenopelmatidae), which despite their name are native to this area, lurk quietly in these dark, moist places. They may be up to three inches long, almost cartoon-like in their bumbling largeness. Recently, entomologists discovered that these fascinating creatures exhibit species-specific ground-drumming patterns. The male plays a rhythmic serenade for the female, who responds only to the song of her own species.
As the hot, dry summer weather approaches, sometimes the only activity visible to the hiker is that of grasshoppers (Trimerotropis sp.: Acrididae and Arphia sp.: Acrididae), which flash their yellow or orange hindwings as they fly.
Earwigs (Order Dermaptera). There is only one native species of earwig in California and its range does not extend to northern California. Nonetheless, a representative of this order in the form of the introduced European earwig (Forficula auricularia: Forficulidae) occurs in the reserve.
Cicadas, leafhoppers, and aphids (Order Homoptera). Aphids, leafhoppers, and lace bugs inhabit trailside shrubs and other types of vegetation. To truly appreciate these minute, delicate organisms, bring a hand lens for better viewing.
A sound associated often with hot summer afternoons is the electric buzz of male cicadas. Though clearly audible, these swift and elusive creatures often evade observation.
True bugs (Order Hemiptera). Though most insects in the reserve are ephemeral inhabitants, the bordered plant bug (Largus cinctus: Pyrrhocoridae) is a dependable resident that can be found throughout the reserve in all seasons. These medium-sized, dark insects with a distinctive red outline seem to crawl about continuously and aimlessly. Stinkbugs (Pentatomidae) also occur in the reserve, and, as their name implies, they secrete a noxious odor if disturbed. Green stink bugs (Chlorochroa sp.) are herbivorous and cryptically colored to match the plants they feed on.
The spotted assasin bug (Rhynocoris ventralis: Reduviidae), a medium-sized, eye-catching black and red or tan bug, is widespread in the reserve. Spotted assasin bugs are sit-and-wait predators, which means that they do not chase down their prey as would a dragonfly but wait patiently for their prey to come to them as would a spider.
Lacewings and antlions (Order Neuroptera). Green lacewings (Chrysopa sp.: Chrysopidae) are among the most common insects of the reserve. The golden-eyed adults flutter about on intricate, gossamer wings that belie their predaceous nature. When walking on sandy or loose, dry soil, keep an eye out for conical pits. Larval ant lions (Myrmeliontidae) dig these pits and wait at the bottom for unfortunate insects to tumble in. Adult ant lions look superficially like gray damselflies with clubbed antennae.
Beetles (Order Coleoptera). Beetles, the most diverse group of macroorganisms on the planet, can be found in almost every possible microhabitat in Cold Canyon. You may spot either predatious or herbivorous ground beetles creaping around the canyon as you hike; however, most most of them hide in the leaf litter or under rocks during the day and come out only at night. One interesting ground beetle, the snaileater (Scaphinotus sp.: Carabidae), flaunts a long snout used to capture its prey of snails and worms.
Large, shiny black stink beetles (Eleodes sp.: Tenebrionidae) spend much of the day hiding under rocks and duff and have the amusing habit of scurrying about with their back ends raised much higher off the ground than their heads. Under harassment, stink beetles emit a noxious fume to deter intruders. In autumn, view the spectacular swarms of ladybugs (Hippodamia convergens: Coccinellidae) that converge in tree hollows and other protected sites.
The only known endangered species inhabiting Stebbins Cold Canyon is the California elderberry longhorn beetle (Desmocerus californius dimorphus). The larvae of this species live in the core of elderberry trunks during their growth and maturation. The attractive grayish black adult beetle is almost an inch in length and has striking orange accents.
Butterflies and moths (Order Lepidoptera). A spectacular diversity of butterflies of all different shapes, colors, and sizes occur in the reserve. Many are showy and can be spotted flying along the path, nectaring on flowers, or mudpuddling near the stream crossing.
The pipevine swallowtail (Battus philenor: Nymphalidae), a spectacular large, black butterfly with an iridescent green shimmer, courses up and down the canyon walls, especially in the spring. Its large purple caterpillar, covered with red fleshy spines, can be found eating California pipevine in the canyon bottom. Another conspicuous species, the California sister (Adelpha bredowii: Nymphalidae), is about the same size as the pipevine swallowtail. It is brown with a diagonal white stripe and a large orange eye-catching blotch near the tip of each forewing and can be spotted soaring lazily among the oaks. In autumn, the buckeye (Junonia coenia: Nymphalidae), a medium-sized brownish butterfly with intricate, multicolored "eyespots," and the acmon blue (Plebejus acmon: Lycaenidae), a beautiful delicate blue butterfly the size of a child’s thumbprint, may be extremely numerous on blossoms of coyote brush.
One distinctive day-flying moth species, common in the reserve in the spring, is the green bumblebee hawkmoth (Euproserpinus phaeton: Sphingidae), a convincing mimic of its namesake. In the late spring, grassy sunlit spots flicker with the presence of the three-striped longhorn (Adela trigrapha: Incurvariidae). The hair-like antennae of this tiny, silver-striped moth are several times its body length, giving it a distinctive appearance.
Flies (Order Diptera). Among the most primitive and unusual of the flies are the crane flies (Tipulidae). Although because of their appearance they are sometimes referred to as "giant mosquitoes," they do not sting. However, like mosquitoes, they are nearly ubiquitous in cool, moist microhabitats.
Common dance flies (Rhamphomyla sp.: Empididae), which have small heads and may have smoky wings, can be found in the springtime. If you look at the males closely, you may discover the small, frothy prey balls they carry, which they present to the females as part of a courtship ritual. The prey balls may contain a variety of smaller insects captured by the males.
Among the biting flies of the reserve are the snipe flies (Rhagionidae). Common snipe flies (Rhagio costatus) attack exposed human limbs and inflict a painful wound. Adults are just under an inch in length, relatively hairless, and dull orange in color. Their natural hosts are probably the many non-human mammals of the reserve.
For a surprising lesson in mimicry, carefully observe the insects visiting flowers for nectar. Many that appear on first glance to be bees are in fact bee flies (Bombyliidae), which have evolved to look like bees presumably to avoid predation. These fascinating flies are delicate and fuzzy as adults, and swift on the wing. Many species of adult bombyliids take flower nectar and pollen as nourishment and may play a role in pollination. The larvae are parasitic on the immature forms of other insects, such as grasshopper egg capsules and cavity-dwelling larvae of certain bees and wasps. One of the most common species in the reserve is the greater bee fly (Bombylius major). Adults emerge as soon as trailside flowers begin to bloom. It is a bulbous, dark, fuzzy fly, not unlike a fisherman's fly, and is often seen hovering over flowers or basking in moist, open areas near the trail. The front of each wing has a sharply margined dark brown blotch, and the rear of each wing is transparent.
Sawflies, parasitic wasps, ants, bees, and wasps (Order Hymenoptera). This order contains an exciting diversity of insects with a huge range of appearances and behaviors.
Sawflies (Tenthredo sp.: Tenthredinidae) are present but not common in the reserve. Many species in this group exhibit parthenogenesis, wherein the females produce eggs without mating. All of the offspring are consequently female, and many of these species have no males. The adults are rust red to black with a large, rectangular head, and the juveniles look caterpillar-like.
An enormous group within this order is the parasitic wasps. Species that parasitize plants are known as parasites, those that parasitize other insects are known as parasitoids, and those that parasitize other parasitoids are called hyperparasitoids. Members of each group occur in the reserve, but because they are small and often cryptic, you may have to observe carefully to find them. The most reliable place to find parasitic wasps is on the oak trees of the reserve, where gall wasps (Cynipidae) occur in bewildering diversity. When looking at oaks, remember that they reproduce by acorn, so any non-acorn protrusion on the stems or leaves is a gall. Gall wasps induce the formation of tumor-like galls, whose shape is usually species specific, and the larvae eat only the tumorous plant material.
Parasitoids (Braconidae, Ichneumonidae, Chrysididae, and Mutillidae) have an interesting life history: the adult female deposits her eggs in the egg, juvenile, or adult form of another insect. The eggs then feed on the other insect, eventually killing it, but generally leaving its skin intact. The carefully observant naturalist may see an adult parasitic wasp then emerge from a beetle larva or an adult aphid. Another good indicator of parasitoid activity is rows of white parasitic wasp cocoons lining a caterpillar’s back.
Watch for the distinctive gray spherical nests of paper wasps (Vespula sp.: Vespidae and Polistes sp.: Vespidae). Paper wasps, the only paper-makers on the planet besides humans, mix wood pulp with saliva to create their nests. Paper wasps, also known as yellowjackets, tend to be black and yellow and deliver extremely painful stings. Most are predatory on other insects.
Among the most spectacular wasps are the thread-waisted or digger wasps (Sphecidae), which are mostly ground-nesting predators. The green cricket hunter (Chlorion aerarium), a metallic, blue-green monster up to an inch and a half long, can occasionally be seen dragging paralyzed crickets along the ground to its cloistered young.
The reserve supports an amazing array of bee species. The European honey bee (Apis mellifera: Apidae) is a widely recognized introduced species with a well known complex social order and communication system. However, many other bee species occur in the reserve as well, and it is exciting to notice them at nectar sources. Two bumble bee species (Bombus edwardsii: Apidae and B. vosnesenskii: Apidae), which are densely hairy yellow and black social bees, are extremely important members of the community because they are able to pollinate many native flowers that the introduced honey bees cannot. Another interesting and common group of bees are the metallic leafcutter bees (Osmia lingnaria: Megachilidae), which are bright metallic blue and live in solitary burrows, not colonies.
Ants (Formicidae) can be pivotal members of communities, scavenging large quantities of
organic matter including dead and living insects, and plant seeds. One of the more common
ants in Cold Canyon is Messor andrei, a seed-harvesting species, whose workers are
black and about 6 mm long. In the summertime these ants consume prodigious numbers of
plant seeds, and leave large accumulations of seed chaff around their nest entrances.
Several species of carpenter ants (Camponotus sp.) also abound in the reserve. Camponotus
semitestaceus is a common ground-dwelling species, which nests both in rotten logs and
directly in the soil. The workers of this species are orange-brown in color, with a
contrastingly darker head, and vary in size from about 7 to 12 mm in length. The reserve
is also notable for its lack of non-native ant species, including the pestiferous
Argentine ant (Linepithema humile). This ant was accidentally introduced into North
America in the late 1800's and it quickly spread across the continent, outcompeting native
ants in its wake. Its absence from Cold Canyon is partly a reflection of the relatively
undisturbed nature of the habitat.
For a more complete list of ants in Cold Canyon, look at the ant
checklist.
Last Updated 03/09/06