Defense, Aggression, and Pogos as Prey
Wrestling and stinging
ants, lunch for spiders, and territorial wars. Pogonomyrmex spp.
ants at various locations in North America.
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Pogonomyrmex salinus
● NW of Mattawa [Grant Co], WA USA [el. 152 m / 500 ft] view location in Google Maps » ● 9/4/08 7:57AM sunny, air temp: 20°C / 69°F
[IMAGE 2 of 2] A western black widow spider (Latrodectus hesperus, juvenile female), with two recently ensnared P. salinus
workers. Based on our observations, these theridiid spiders are frequent predators of P. salinus ants in central Washington State. After the initial attack (which we apparently just missed), the spider pulled the ants up into a tangle of dry tumble mustard (Sisymbrium altissimum), approx. 40cm / 16in above the ground. [scroll down for additional notes/references]
ADDITIONAL NOTES/REFERENCES:
To verify the sex of this spider, we captured this individual alive - it developed into a typical (glossy black with red ventral 'hourglass') adult female western black widow (Latrodectus hesperus), in captivity. The coloration and markings of widow spiders (Latrodectus spp.) are highly variable until the adult stage is reached.
Based on our observations, juvenile western black widow spiders (Latrodectus hesperus) are frequent predators of P.salinus ants in central Washington state. We have not observed any adult L. hesperus preying on Pogonomyrmex salinus, nor have we seen any near the ants, or their nests. This is consistent with the findings of MacKay, in his study of L. hesperus and Pogonomyrmex rugosus, where it was observed that females apparently stop feeding on ants when they become adults (according to McKay, it is possible that males continue to prey on the ants throughout their lives, though as noted above, we have not yet observed this).
Latrodectus hesperus spiders often position themselves in a web just outside the entrance to a Pogo nest. Pogos have been known to close a nest entrance, and open a new one a short distance away, to avoid these predators. Some species, like Pogonomyrmex rugosus, may stop foraging altogether (living on stored seeds), until a spider (or spiders) leave the vicinity of the nest (L. hesperus will move to an active nest nearby, if this occurs). We have seen evidence of these behaviors in Pogonomyrmex salinus (in central WA) as well, with web-covered entrances apparently blocked with debris by the ants, and no foraging activity occurring. Despite their powerful mandibles and formidable stings, Pogos do not appear to be able (or willing) to attack, kill, or repel these predators directly - relying instead on the more passive methods of avoidance mentioned above. We have also observed P. salinus workers attempting to remove webs (most likely webs of L. hesperus) from the vicinity of the nest entrance, however in these cases, no spiders were present.
In areas where we observe western black widows preying on P. salinus, it is usually evident that the spiders are not specializing on ants to the exclusion of all other food sources, as we occasionally see the remains of beetles, and other insects in their webs.
·MacKay, W. 1982. The Effect of Predation of Western Widow Spiders (Aranea; Theridiidae) on Harvester Ants (Hymenoptera: Formicidae). Oecologia (Berl) (1982) 53:406-411
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