All I can find that looks like them is black ground beetles. They seem to have gone now. I put some sevin dust on the ground around the plants, and haven't seen anymore, but there isn't anything ripening right now. They are only attacking one kind of tomato - my Park's Whoppers. I planted these tomatoes in the free compost from the county. Do you think the eggs/larvae could have come from there? I've never seen these before.

Control of Squash Vine Borers and Squash Bugs is multifaceted, there is no one method, substance, or other means of control that is 100 percent effective. Nematodes can help, for the larva that are in soil where the nematodes dwell, but they are of little value if the eggs are laid on the plants and the larva stay on the plants. Floating Row Covers, early on, can help, providing a good habitat for predators of these wee buggers can also help, insectaries. Very carefully using any pesticide, most will kill any beneficials, is also of importance. Here is a link that might be useful: Squash bug control

Definitely stay away from those chemicals, tristate!! I use row cover (old nylon curtains from garage sales/Goodwill work great) from the time of setting out the seedlings or as soon as the first seed pops its little neck out of the ground just to be safe. AND I choose cultivars of squash & cucumbers that are parthenocarpic--a $10 word for self-pollinating -- so I never have to remove the covers except to harvest. No problem whatever with heat or moisture buildup; there is sufficient airflow to prevent that. No reason to uncover the plants until you see FEMALE flowers starting to appear. The male blooms generally precede the fruiting flowers by maybe a week. 'Course, those are the ones to pick for stuffing anyway! In your case, assuming you are not growing the self-pollnating kinds, it is my understanding that if you remove the protective covering very early in the morning and leave it off for a couple of hours, it gives the bees time to pollinate and the flowers close by noon-ish naturally anyway, so back on go the covers. Or you could pollinate in the morning by hand using a soft paintbrush then re-cover the plants as soon as you are through. :-) I also use Reemay over my eggplant from the moment of setting them out; I think that flea beetles--my nemesis when it comes to eggplant--would manage to get thru tulle. I use tulle instead of bird netting on my blueberries, though, as it is easier to work with than the netting, which gets all tangled on the branches. One last suggestion: it seems that cucurbits seeded later in the summer (say after July 4, but depends on your geographic location) are less prone to insect pest attack and since they are pretty fast-maturing you still have plenty of produce to harvest before the growing season ends even if you are not the first kid on the block to have squash & cukes. (Hey, if the insects get everyone else's early plants, you may be the ONLY kid on the block with produce! LOL) If you check with your local extension office, they can give you dates of pest species emergence/disappearance. Good luck--and next year search out the parthenocarpic cultivars. I plant Diva cukes, which I like very much.

A picture would be very helpful.