Insects, spiders and other arthropods form the great majority
of animal species on Earth. The number of described species of
arthropods worldwide is almost 900,000 (out of just over a million
animal species), and there are thought to be 5 million to 50 million
yet to be described! Arthropods are integral to many ecosystem
functions, such as pollination by bees, butterflies, flies and
beetles. breakdown and recycling of organic matter by spiders,
mites, and insect larvae, and predation on herbivorous insects
by bugs, beetles, dragonflies, wasps and flies. Insects also are
a key food item for many birds, mammals, reptiles, and amphibians54.
ongoing study at Quail Ridge and other nearby localities highlights
the ecological role of arthropods. Bees are important pollinators
not only of wildland flowers that produce habitat and food for
other wildlife, but also of commercial crops. Recently there has
been concern about declines in populations of the European honeybee
and other important crop pollinators. But a survey of farms and
natural habitats along the western edge of the Central Valley
shows that wildlands, such as Quail Ridge, support a rich diversity
of native bees that provide pollination to bee-dependent crops
such as tomatoes and melons on nearby farms46.
Despite the importance of arthropods, we do not have a full list
of the species for Quail Ridge or for virtually anywhere else
on Earth. Many groups of species have not yet been fully classified,
and even most nature reserves have not been thoroughly surveyed.
However, Professor Lynn Kimsey and her Entomology 107 class made
a good start in 1997, 1999, and 2001 by compiling a list of the
insect families they collected at Quail Ridge (Insect
List). With 132 families, it falls short of the 221 recorded
at Stebbins Cold Canyon, probably because there are fewer streamside
habitats at Quail Ridge, but also because there has not been as
much collecting yet.
How many arthropod species might there be at Quail Ridge? We
can get an estimate by considering the survey of butterflies and
moths (order Lepidoptera) conducted at Quail Ridge by Greg Kareofelas
and Bill Patterson. In over ten years of netting the day-flying
species and capturing the nocturnal ones by blacklighting (where
moths and other night-flying insects come to rest on a white sheet
hung next to an ultraviolet light), these dedicated lepidopterists
found just over 500 species (Moth
List). Since Lepidoptera typically comprise about 15% of all
insect species in a locality or region41,
we can predict there to be about 3,300 insect species at Quail
Ridge. Add another 400 mites, spiders, and other arthropods, and
we get a total of nearly 4,000 arthropod species – nearly
80 times the number of mammal species thought to occur at the
In this section we will briefly describe the major kinds of arthropods
likely to be found at Quail Ridge, emphasizing insects since they
are the largest and best-studied group. We conclude with some
suggestions on how to go and see interesting insects at the Reserve.
What are Arthropods?
Arthropods are invertebrate animals with a hard chitinous exoskeleton,
jointed appendages, and a body that is composed of segments. These
segments are themselves grouped into major body regions (tagmata),
for example the head, thorax, and abdomen of insects. All arthropods
undergo periodic molting to grow out of the confines of their
rigid exoskeleton. There are four major groups of arthropods:
Spiders, mites, and relatives (chelicerates) have
two tagmata, usually 4 pairs of legs, and no antennae.
Sow bugs, pill bugs, and their aquatic relatives (crustaceans)
have many legs and two pairs of antennae.
Centipedes and millipedes (myriapods) have two tagmata,
many legs, and one pair of antennae.
Insects (hexapods) have three tagmata, three pairs
of legs, one pair of antennae, and usually one or two pairs
There are also other less conspicuous invertebrates at Quail
Ridge, such as earthworms (annelids) and snails and slugs (molluscs).
See The Natural History of Stebbins Cold Canyon Reserve45
for more about these non-arthropod invertebrates.
More About Insects
Insects are easily the most diverse and abundant group of arthropods.
They are the only invertebrates to evolve wings, which perhaps
helps explain why they are so successful. Also, most insects have
complex metamorphosis that allows their immature and adult life
stages to occupy different habitats and use different resources.
The most advanced insects, including beetles, wasps, butterflies,
and flies, have a “holometabolous” life cycle with
four stages (egg, larva, pupa, and adult). During the pupal stage
a remarkable transformation occurs as the maggot or grub-like
larva becomes a winged adult. Other insects have a “hemimetabolous”
life cycle with three life stages (egg, nymph, and adult); the
nymphal stage may have several substages (instars), each one a
larger version of the one before.
Example of holometabolous development,
with four life stages (egg, larva, pupa, adult), as seen in endopterygote
Insects in strongly seasonal environments may produce one or
several generations every year, but typically become dormant during
the unfavorable season. In California’s Mediterranean climate,
winter and spring are the time of feeding, growth, and mating
for most species, followed by dormancy in summer and fall. Depending
on the species, the dormant stage may be the egg, larva, pupa,
or adult. A few species, such as the tortoise-shell butterfly
(Nymphalis californica), undergo spectacular migrations to take
advantage of spring conditions at higher elevations after summer
has begun at lower elevations.
Example of hemimetabolous development,
with three life stages (egg, nymph, adult), as occurs in exopterygote
A good reference for learning basic insect identification is
the Peterson Field Guide to Insects42;
try the pictorial key to orders on the front and back endpapers.
Other useful field guides include California Insects49;
National Audubon Society Field to Guide to North American Insects
Peterson Field Guide to Western Butterflies; Sierra Nevada Natural
The Natural History of Stebbins Cold Canyon Reserve45.
More technical keys to insect families can be found in An Introduction
to the Study of Insects41.
Photo Credits: Title, Giant Water
Bug (Mike Benard), Honey Bee (Joyce Gross), Swallowtail (Gerald
and Buff Corsi), Life stages (Hickman et al. 2001). For more pictures