Tarantula Behavior and the Monsoons

The arrival of the summer monsoons is always a big event in the high desert of New Mexico.  Working with the law of the minimum the rains awaken the desert and the wildlife explodes across the landscape.  From the emergence of frogs and toads singing for mates at ephemeral pools to the ants on their mating flights, the desert suddenly becomes alive with the rains.

One of the species visible on the landscape are the tarantulas (Aphonopelma sp.).  A large female has maintained a burrow by the garage for years, and is always a good indicator of monsoon season.  She digs herself out every year and can be found mating just before the start of the rains, (video).  A second female has established a burrow about 100 ft away by a concrete pad and both have mated several times this year with local wandering males.

A new behavior was observed in these insects with the first significant rain of the season.  The estate received 0.15" the other afternoon and while out wandering in the rain both females were observed sitting partially outside their respective burrows, see images below.  Curious as to this behavior observations continued (yes, I was standing around in rain watching insects).  Seeing females out during the day is unusual and their position suggested they were either blocking their entrance from the rain or funneling water to drink.  As the rain subsided the female by the garage emerged completely from her burrow, circled the entrance, and went back inside.  The other female also retreated into her burrow after the rain stopped.  A single male arrived approaching one of the burrows, but the female did not respond or emerge, so the idea of a mating behavior was discarded and it was concluded that the entrance sitting behavior was not associated with mating but rather related to the rain.

Several days later the estate received another rain, 0.53".  This rain came in several waves.  The first (0.03") did not elicit any response from either female and they stayed well inside their burrows.  The second wave of rain (0.13") was rapid and flooded the entrance to one burrow but at the other burrow the female could be seen in throat of the burrow but not partially emerged as noted during the previous rain.  During a lull in the rain the burrow that was flooded was again open and the female observed sitting in the throat of the burrow.  With subsequent waves of rain neither female repeated the partial emergence behavior but continued to sit in the throat of their respective burrows.  Though after the rain one female did completely emerge and circle the entrance before reentering and disappearing, see last image below. 

It is still not clear whether the entrance sitting behavior is related to capturing water for drinking or a burrow protection behavior.  But it is clear that Tarantulas also like the rain.

Female Tarantula by the garage.

The newest female Tarantula sitting in her burrow.

Female emerging after the rain