Looks like rat to me. Watermelon seeds are too small of an incentive for squirrels. Get a cat or two! They are much better than dogs at deterring rodents because they are proactive. I have 3 of them and they spend 90% of their time napping in my garden: squirrels stay at bay, possums also ( except for one that they tolerate on the fence only - not on the ground-) birds do not pick my fruits or vegetables, no rats, no mice = peace of mind. With nectarines, apricots, grapes, plum, pears, tomatoes, cantaloupes, watermelon etc, in my garden, there would be rodents all over the place if it wasn't for them! If you do not want a cat as a pet, associations are giving "barn cats" they are neutered microchipped and vaccinated, they live in barns/sheds and they do their hunter job. But you need to provide a safe place where they can go when it is too cold or too hot, water, food, vaccines, and vet care. Mine are well fed and are spoiled pets so they don't "over hunt" and sleep on our beds. They run after pests but stop the chase as soon as the critters are out of the garden. Good balance. Squirrels are staying high in the trees ( I like squirrels as long as they don't eat my fruits) I keep a stepladder in between my tomato plants, the cat lays on the upper stair and the birds do not even think about my tomatoes: problem solved.

Is the culprit? Or this? Both are pictures of armyworms. You don't want them on your plants, as you've discovered. Bt will dispatch them quickly and thoroughly if that's what they are.

John, Thanks for the reply. That .pdf looks like a really nice resource. I have several species of spiders all over the garden, nothing specifically targeting pinworms. I am pretty sure that the most common variety I have is a yellow sac spider. The spiders may not be helpful with pinworms that have buried themselves inside the plant or fruit, but they do a nice job of killing off the adult moths and random traveling pinworms. The spiders combined with diligent human search and destroy techniques (targeting pinworms with minimal leaf removal) have worked well for my small kitchen garden (~9 tomato plants, ~25 plants overall). -Chris

Alan - When you go shopping for any product, read the label first and see if it is safe to use it. You can find at any big box store the following products that I have used it before, remember there is no one cure for all, but it helps. Neem - use it as a fungicide and some insect control BT - use it for caterpillar control Currently I am using serenade for disease and spinosad for some bugs. When I mix the 2 together, I also add a few drops of Dr Bonners castile peppermint soap. I copied this recipe long time ago from Al (container forum) he said uses for whitefly, personally I have not used it. 1 quart 1 pint very hot water 1 teaspoon neem oil (cold pressed or virgin only) 4 drops Murphy's oil soap (or dishsoap) Shake well and add 1 pint of 70% isopropyl (rubbing) alcohol Shake frequently while spraying. When using any new product or recipe try it on a few leaves and see if it is safe for the rest. I don't spray flowers or herbs. Hope it helps. Silvia