Castianeira alteranda

Catianeira alteranda is an ant-mimic spider without a common name if the spider family Corinnidae. These sac spiders mimic ants with their size, appreance and behavior to get close to them and prey on them. They are found in the Rocky Mountains of the United States and Canada.

Quick Overview: Castianeira alteranda
Medically significant: No
Body size: 0.23-0.4 in (5-10 mm) in length
Main colors: Brown, Black, Orange
Range: Rocky Mountains (United States, Canada)
Web: No web

Castianeira alteranda Description

As many species of ants, the primary color of C. alteranda is usually a reddish brown, orange or red. While their overall appearance can be quite variable, their cephalothorax (head) is almost always uniformly colored in a reddish brown or orange color. Their abdomen is shiny and oblong, mostly reddish brown or orange, sometimes even red, and may have black transverse stripes. The stripes are sometimes broken in the middle.

The stripes give the illusion of a third body segment like an ant has. The pattern and colors often appear almost tiger-like.

Castianeira alteranda found by Jennifer in Polson, Montana Orange spider with black stripes tiger spider ant mimic
Castianeira alteranda found by Jennifer in Polson, Montana

The color of the legs can range from uniformly orange/brown to translucent brown/cream and even entirely black or black with white bands.

Their appearance is almost identical to that of their close relative Castianeira amoena. These two species can be distinguished by their range. While C. alteranda occurs in the Rocky Mountains, C. amoena occurs in the Southeastern United States.

Size

Castianeira alteranda is a small species of spiders. They often look much larger in photos than they are in real life. The body size of an adult specimen is between 0.2-0.4 in (5-10 mm).

Range of Castianeira alteranda in United States
Rare photo of Castianeira alteranda. Photo by: Steven Mlodinow

Web

These spiders do not make webs to capture their prey. Thanks to their appearance and ant-like behavior, they can move close to ants without raising any attention. They will lift their two front legs up to appear like antennae and walk on six legs like ants. Once close enough, they will strike and immobilize the ants with a venomous bite.

Castianeira alteranda spider bite

Like any other spiders, these ant mimic spiders usually bite for defense but are generally not harmful to humans. They are not considered medically significant. A bite, if the small spider even manages to pierce through human skin, may lead to some local swelling and itching.

Castianeira alteranda spider Scientific Classification

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Chelicerata
  • Class: Arachnida
  • Order: Araneae
  • Infraorder: Araneomorphae
  • Family: Corinnidae
  • Genus: Castianeira
  • Species: Castianeira alteranda

Distribution of Castianeira alteranda in the USA

Castianeira alteranda is found in the Rocky Mountain areas of Colorado and Montana as well as in Alberta, BC, Canada.

Castianeira alteranda

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