Page 501 - The Book of Caterpillars: A Life-Size Guide to Six Hundred Species From Around the World

MOTH CATERPILLARS

FAMILY Geometridae
DISTRIBUTION Across southern Canada, from Vancouver Island to Nova Scotia,
south to much of the United States, excluding California
HABITAT Deciduous and mixed wood forests and woodlands
HOST PLANTS Douglas Fir (Pseudotsuga menziesii), willow (Salix spp.),
White Birch (Betula papyrifera), hazelnut (Corylus spp.), and
others; occasionally on crops such as strawberries (Fragaria spp.)
and carrots (Daucus spp.)

NOTE Caterpillar that has two pairs of long laments, or tentacles
CONSERVATION STATUS Not evaluated, but common in riparian habitats in parts of
its range

ADULT WINGSPAN
¾–1 in (20–25 mm)
CATERPILLAR LENGTH
1½–2 in (38–51 mm)
NEMATOCAMPA RESISTARIA
HORNED SPANWORM 499

HERRICH-SCHÄFFER, [1856]

The Horned Spanworm, also called the Filament Bearer, is
named for its unusual caterpillar, which bears laments on three

of the abdominal segments. The laments are initially short but
increase in length as the caterpillar grows. Their function is
not clear, but the sensory hairs on them suggest that they may,
for instance, help the larva to detect vibrations produced by an
approaching predator. Alerted, the caterpillar would then stop

moving; at rest, it is well camou aged as the laments provide
additional structures that make it look much like a twig.

The moth is also cryptically colored, with colors and a pattern
that make it practically invisible against a background of
fallen leaves. As a member of the inchworm moth family,
Geometridae, which are mostly cryptically colored and
palatable, Nematocampa resistaria is an essential part of the food
chain: birds feed on Geometrids, and especially during colder
months, when other insects are less abundant, this moth becomes
an important food source.

The Horned Spanworm caterpillar has
distinctive abdominal projections, or Actual size
laments, located dorsally. Otherwise,
the caterpillar resembles other inchworms,
being a reddish-brown color with a lighter,
cream-colored pattern that helps it to
blend in with the twigs of the trees on
which it feeds.