The caterpillars are very hairy, about an inch long,
pale yellow with black spots, and they fill the webs with black pellets of
excrement. They winter in cocoons under trash on the ground or under
tree bark, and the moths lay eggs on leaves in spring. The first generation webs and feeds for about a month, in June, and the second generation
works in late summer, its webs being more numerous and spectacular
than those of the first brood.
Control. For small ornamental trees it is quite feasible to cut off the
webbed branches and burn the nest. The spray schedule for codling moth
controls web worms on apples; on shade trees either DDT or lead arsenate
is effective if applied when the caterpillars are only half grown.
JUNIPER WEBWORM (Dichomeris marginella).
Needles of some juniper
varieties are webbed together with silk enclosing reddish-brown
caterpillars and a large amount of frass. Sometimes the whole top of a
small juniper is webbed together with branches turning brown, sometimes dying. Moths lay eggs in June in new terminal growth, and half-
grown larvae winter in silken cases in webbed foliage.
Control. Cut out webbed masses where possible. Spray in summer when
larvae are young with DDT (adding a miticide to prevent build-up of
spruce mite) or with lead arsenate. In spring try pyrethrum or nicotine
sprays applied with force enough to break webs.
PINE WEBWORM (Tetralopha robustelld).
Needles near the end of terminal
twigs are webbed together with silk containing conspicuous masses
of brown frass. If you pull these webs apart in early June, you can
usually find hiding rather fat, inch-long caterpillars, olive green with a
brown stripe along the body. I have seen young pines severely injured;
larger trees are somewhat disfigured but not really harmed. A DDT
spray applied in May should help; by the time people notice the webbing
and frass, the insect is signing off for the season anyway.
SOD WEBWORMS (Crambus spp.).
These are the lawn moths that fly up in
a zigzag motion when you walk across the grass at dusk. They
have a pronounced projection from the head, are golden to pale brown,
and when at rest their wings are folded so close to the body they look
like little cylinders. The fat larvae, much like cutworms, live in silk-lined
tunnels or tubes in the soil. The young caterpillars skeletonize grass
blades, and older larvae cut them off.
Control. Apply 5% chlordane dust, or water the soil with lead arsenate, using 1 pound to 200 square feet. Pyrethrum or dichlorethyl ether
sprays can be used for temporary control.