Squash Bug

Anasa tristis

Squash bugs are one of our more problematic pests of cucurbits, particularly summer and winter squash and (usually to a lesser extent) cucumbers. Damage occurs from direct feeding injury, and in addition, squash bugs can serve as a vector for plant disease. Squash plants often decline rapidly when squash bug populations boom.

This is an adult:

Females lay clusters of eggs on plant leaves, usually on the cucurbit plants where the young will feed. Very recently laid eggs tend to be pale in color, such as these:

Eggs turn to a darker shade of red/brown as they get closer to hatching. Most of the time, eggs are laid on the underside of leaves, as shown here:But sometimes eggs are on the upper leaf surfaces, as shown below on a large squash leaf, which provides a sense of scale. Learning to spot the eggs is useful, because physical removal of the eggs is one of our preferred control options to keep population numbers in check. Eggs are vulnerable because they’re not mobile, and we can systematically work our way through a squash planting looking for and squashing the eggs. Eggs take 10 days +/- to hatch (depending on what source you believe; we don’t have our own data for this).

Here are some nymphs that have just hatched:

After a molt, nymph coloration changes to grey, and several more molts take place before adulthood.

Then as adults, the whole cycle begins again:

During the growing season, we most often find adults hanging out along the base of the main stem of the squash plant, close to where the stem emerges from the ground. Another favorite hideout is on the underside of large squash leaves that are touching the ground. When searching for eggs, we also seek out adults & nymphs and squish those, too. The smell of a squished squash bug is rather unpleasant.

During the winter, we’ve found adults taking shelter in weed piles and straw bales, often in the vicinity of the late summer squash planting.

Toads are confirmed predators of squash bugs. In late summer of 2012, I watched an American toad eat an adult squash bug. The squash bug virtually crawled across the toad’s nose. The toad seemed to wait for just the right moment, then, gulp, it was gone. Hooray for toads.