Picture ID 118096

Picture of unidentified spider

Comments & ID Thoughts

Found this spider in hot tub today, really want to know if it’s poisonous and what to do with it, please help! Thank you! We live in Colorado.

  • Submitted by: 
  • Submitted: Jul 28, 2020
  • Photographed: Jul 28, 2020
  • Spider: Unidentified
  • Location: Boulder , Colorado, United States
  • Spotted Outdoors: Man-made structure (building wall, fences, etc.)
  • Found in web?: No
  • Attributes:
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Hi there this looks like a red-back spider or a male black widow :3


Hi there. This is Castianeira crocata, an ant-mimic spider. It is harmless.

Keys for identifying black widows include:

  • Body shape – Black Widows have nearly spherical bodies.
  • Color – Black Widows are invariably glossy.
  • Leg shape – Legs are long and the tips curve inward, ideal for clinging to webs but suboptimal for walking on the ground. They are not fast runners.

There are no redback spiders in Colorado, but juvenile Western Black Widows can have red stripes on their backs.


I found one of these outside my house just a couple hours ago. It is indeed Castianeira Crocata. They move way too quickly on the ground to be black widows. All spiders are venomous but the widow and the brown recluse are the only ones whose venom you should be remotely worried about here in the States.


I just followed one of these across my patio in Northglenn, CO. It was much too fast to get a photo, but it certainly looked the same as the one in this photo.