Asked July 15, 2015, 11:47 AM EDT

Noticed a dot on my ceiling two nights ago. Came home the next night and the dot looked smeared. after further inspection I found what appears to be some sort of feeding sack surrounded by what looks to be spiders. Im not sure if they are spiders as for some of them look like they have antennae. Not having much success in finding out what this is...

Weld County Colorado spiders

1 Response

The objects in your photo are not spiders. The dot on your ceiling was a cluster of eggs, and what has hatched out of it are nymphs (babies) of a type of assassin bug (Order: Hemiptera, Family: Reduviidae). Unfortunately, I cannot identify the genus or species from the tiny nymphs in the photo, but I suspect that they might belong to a species in the common genus Zelus. Assassin bugs are ambush predators on other insects. They have beak-like mouthparts which they use to inject a paralyzing saliva into their prey. The saliva also begins to digest the internal body parts. The assassin bug then sucks out the body fluids as its meal. The front legs are thickened and slightly modified for grasping, which helps them subdue their prey. These newly hatched babies also have disproportionally long antennae as you noticed, which could easily be mistaken for another pair of legs on a spider. Because they are predators, assassin bugs are generally considered to be beneficial. However, if carelessly handled, they can use their beak and saliva to inflict a painful sting-like "bite". Normally, assassin bugs would be found outdoors and would lay their eggs on the bark of trees, under rocks, or on the ground. I suspect an adult female assassin bug was attracted to lights in your house and once inside just chose to lay her eggs on the ceiling. Without tiny insect food and moisture, these babies will probably not survive long inside your house. If they are still clustered on your ceiling you could gently brush them off into some kind of container to carry them outside to let them go. I have included a link below to a website with more information about these bugs. On that site, there is a picture of some slender green assassin bugs in the genus Zelus that you can see look very much like the ones in your photo.