Valerie Blackmore      

Funding:  ASU School of Life Sciences (SOLUR Fellowship)

Territoriality, agonism and cannibalism in black widows

My name is Valerie Blackmore, I am a Junior at ASU and a SOLUR researcher working with Dr. Johnson on the behavioral ecology of black widow spiders, Latrodectus hesperus. I have recently completed a pilot study on territoriality, agonism and cannibalism in female black widow spiders. There are a few main theories regarding territory disputes. One hypothesis predicts that the resident should win because they have invested more in developing a territory and thus have more to lose than an intruder.  Alternatively, the larger competitor may win regardless of territory ownership because it is in better physical condition.  Conversely, the pay-off asymmetry hypothesis states that the winner should be the competitor in the worst condition because they have the most to gain from the encounter and so are willing to risk more .

 I wanted to see which one of these hypotheses was supported in our black widows. For this experiment I used 18 well-fed, lab-reared females that had set up residence. Then 18 intruders which were, on average, 49% of the resident’s weight were introduced into the residents’ web. Surprisingly, in 17/18 trials the smaller intruder killed and cannibalized the larger resident. Only 1 pair showed co-habitation and none showed the larger resident killing or excluding the smaller intruder. Furthermore, 6 of these cannibalisms took place during the first hour the intruders were introduced, 9 within the first 24 hours, and 17 within 5 days. These results appear to support the pay-off asymmetry hypothesis where poor condition females win encounters due to the fact that they have the most to gain. However, many factors need to be taken into account as we proceed. Next we will repeat the experiment this time with intruders outsizing residents.