Disclaimer: Squash lady beetles, aka Squash beetles, are not the same as squash bugs https://bugguide.net/node/view/2026342/bgimage, no matter how interchangeably the BugLady uses the terms.  But, when you Google Squash beetle, you’re soon awash in hits for Squash bugs.

Squash lady beetles (Epilachna borealis) are in the Lady beetle family Coccinellidae and the Plant-eating Lady beetle subfamily Epilachninae.  There are three North American species in the genus Epilachna, and a lot more elsewhere.  Squash lady beetles are found in many of the states from Texas to Massachusetts, but not in Wisconsin https://bugguide.net/node/view/61612/data, and they’re said to be more abundant along the Atlantic Seaboard.    

Besides their diet, the other thing that startled the BugLady about them is that many of our Wisconsin lady beetles have cool patterns on their head and thorax https://bugguide.net/node/view/1448746/bgimage, https://bugguide.net/node/view/2214673/bgimage, https://bugguide.net/node/view/2071575/bgimage, and seeing a lady beetle with a “nude” front end https://bugguide.net/node/view/306884/bgimage was, well, a little unsettling.   

So, what about that diet?  Most lady beetles are carnivores, stalking small, soft-bodied invertebrates over the plant leaves.  They (inadvertently) aid farmers by eating the things that eat the crops.  Squash lady beetles feed on the crops – cucumbers, melons, zucchini, gourds, pumpkins, cantaloupe, and squash.  Both the bristly, little larvae (whose spikes have spikes https://bugguide.net/node/view/341984) and the adults eat the tender tissue between the leaf veins (the larvae only feed on the underside of the leaves https://bugguide.net/node/view/265041/bgimage), but they may graduate to the rind of the fruits when the fruits appear, chewing patterns that remind the BugLady of crop circles (yes – squashes and melons are considered fruits because they develop from the flower’s ovary and contain seeds). 

Squash lady beetles are featured on a whole bunch of Extension Agricultural Bulletins, and although some sources say that they don’t get numerous enough to become pests, cosmetic damage due to their feeding may make produce less sale-able.  Worst possible scenario – leaves skeletonized by large numbers of larvae don’t photosynthesize as readily, plants don’t thrive, and they produce fewer fruits.

Before they tuck into a leaf or rind, the beetle chews a spiral “trench” around the feeding area, a habit that has had scientists scratching their heads.  Originally, it was thought that the trench, like the small, upstream cuts made by dogbane leaf beetles, worked to minimize the plant sap in the area.  Scientists speculated that the chemicals in the sap (cucurbitacin), and the sticky sap itself, hindered feeding.

The BugLady found a couple of papers about this.  One researcher, writing in 1985, concluded that both adult and larval feeding on leaves triggers cucurbitacin in the injured leaf and in its neighbors, and that cucurbitacin repels the lady bug and may stunt the larva, and that the trenches serve to block the movement of the chemicals, temporarily.

A second paper in 1995 (and the author of the first paper was a co-author of the second) concluded that feeding by the Squash lady beetle did not cause a build-up of cucurbitacin, that the presence of cucurbitacin actually stimulates the beetles to feed, and, in fact, ingesting it doesn’t affect the larvae.  It suggests instead that the trenches may act as dams against the plant’s sticky sap, which gums up the beetle’s mouthparts.

Squash lady beetles overwinter as adults under tree bark or under leaf litter at the edge of an agricultural field.  They hike/fly back into the fields when the squash plants are leafing out, feed on the leaves for a while, find romance, and then oviposit on the leaf or vine in July, laying as many as 400 eggs, in clusters of about 45 https://bugguide.net/node/view/547304/bgimage.  The larvae feed, then pupate, on the underside of the leaf, and emerge in late August.  Adults feed for a few weeks before leaving the field and finding a sheltered spot for the winter. 

They have a Super Power. 

Like “regular” lady beetles, they “bleed” from their leg joints when alarmed (reflex bleeding), and that blood repels other insects.  And, oily droplets on the end of the larva’s spikes repel insects.  And, oily drops on hairs on the pupae deter ants.  Despite the chemical protection, stink bugs and assassin bugs prey on them, tachinid flies parasitize them, and lady beetles – including other Squash lady beetles – may eat the eggs.

Here’s the aforementioned Dogbane leaf beetle’s story – https://uwm.edu/field-station/bug-of-the-week/dogbane-leaf-beetle-revisited/

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/