That is a melonworm, a moth caterpillar. They usually like to eat curcurbit (squash, cucumbers, etc.) but will eat other plants if they choose to. The strange thing is watermelon consumption is rare. My brother and I had our watermelons destroyed last year by them. They took out our squash and cukes too. We thought they were pickleworms, which I guess are basically the same. But closer inspection proved otherwise they were in fact melonworms.They will burrow into the stems of your plants if they can fit, and eat the foilage too. I suggest BT as soon as possible before your plants are unsalvageable like ours were.
Here is how he and I got rid of them in a post from last season:
Slept in today and woke up around noon. I decided to go check all my plants as I always do everyday or so. I turned the back corner of my house and (
gasp!) to my horror, I saw my cucumbers and squash were dead as a doornail, overnight. The watermelon wasnt looking so hot either...
So after closer inspection I saw some holes in my first watermelon ever that I had been daily checking the progress on. After a little searching on google images I found out I had pickleworms. They only seem to affect cucurbits , such type plants as cucumbers, squash, and melons. Thier favorite is squash, though. It was time for them to go. I had to destroy all of my plants and promptly burn them. I wont say they didnt put up a fight...they did have the numbers, but it was victory by a landslide. I won.
Guess i'll be picking up some BT soon before this happens again.
The melon:
The worms:
All my hard work, gone:
Weapons of war:
In ya go...:
Light em up:
Watch it go!
Burn baby burn!!
Victory!!
Sorry for the very long post but I think it might be amusing to anyone who sees it. Hope your plants will fare fine after their successful removal. Pests can be a seemingly never ending problem, but you will win the war if you try.