Members of this order include: stoneflies.
Etymology: Plecoptera comes from the Greek words pleco,
which means folded, and Petra, which means wings.This
refers to the hind wings, which lie folded and concealed
beneath the front wings when the insect is not flying.
long, somewhat dorsoventrally flattened body
long, multi-segmented antennae
two long, multi-segmented cerci
two pairs of membranous wings
forewings are long and narrow and fold atop one another
when the insect is at rest, concealing the hind wings
hind wings are slightly shorter, but considerably wider than the
the hind wing’s anal lobe (see illustration) is pleated, which allows
it to fold beneath the forewings
crossveins form two rows of “windowpanes” in the middle of each
hemimetabolous metamorphosis (egg — naiad — adult)
Number of recognized species worldwide: 1,500-3,000
Common Name: Rock Crawlers / Icebugs
Greek Origins of Name: Grylloblattodea, derived from the
Greek “gryll” meaning cricket and “blatta” meaning
cockroach, refers to the blend of cricket-like and cockroach-
like traits found in these insects.
Rock crawlers measure 14–30 mm in length, and are elongate
Mouthparts mandibulate, hypognathous
Eyes are small or absent.
The head is large, consistent with orthopteroids
The antennae are filiform, moderate in length, and shorter
than many crickets and cockroaches.
The legs are unspecialized, and the tarsi have five segments
ending with a pair of claws.
The body segments are clearly differentiated
Development & Distribution
Development: Hemimetabola, i.e. incomplete
metamorphosis (egg, nymph, adult)
Distribution: Rare. Found in caves or near ice or snow at
high elevations in mountains of Asia and North
America. Approximately 1 family and 11 species in North
America and 1 family and 25 species worldwide
Rock crawlers were first discovered around 1906; the first
formal description of the order was published in 1915.
With only 25 species described worldwide, Grylloblattodea is
the second smallest order of insects. Mantophasmatodea is
the only order with fewer species.
Rock crawlers cannot tolerate warm temperatures. Most
species are active below freezing and usually die above 10
Due to the cold temperature at which they live, growth and
development is very slow. Rock crawlers may require up to
seven years to complete a single generation.
No grylloblattids have ever been found in the Southern