JUMPING SPIDERS AS

COMPETITORS/PREDATORS

OF THE HOBO SPIDER

Jumping spiders are fascinating arachnids which belong to the spider family Salticidae. Approximately 4000 species of jumping spider have been described world-wide, with about 300 species in the Americas north of Mexico. The behavior of these spiders has drawn the attention of humans around the globe; jumping spiders have been accredited over the years (rightly or wrongly) with a number of admirable qualities, such as bravery, courage and intelligence. Jumping spiders will watch and follow a finger waved before them, and appear to contemplate each move; their eight eyes are designed for predation, two of the eight being large, giving them vision far superior to most other invertebrates. It has been demonstrated that some jumping spiders can recognize other spiders and prey as distant as eight feet away. Jumping spiders typically pursue and leap upon their prey, and can jump considerable distances in the process; they are capable of moving sideways or backward with great agility. Jumping spiders are primarily diurnal, but due to the prevalence of certain species around buildings and yards, they do come into contact with, and prey upon hobo spiders. As food competitors of hobo spiders, jumping spiders undoubtedly play a significant role.

One of the smaller salticids which is found throughout the North American range of the hobo spider is the zebra jumping spider, Salticus scenicus (pictured above left). Zebra jumping spiders prefer to live on and around buildings in the northern hemisphere (old and new world), and are one of the most common and well known salticid spiders. Remarkably, this little spider, averaging only about 5 mm in body length, has reportedly been observed attacking and killing adult hobo spiders on occasion: In 1997, Eagle Rock Research received two reports of southern Idaho specimens stalking and killing adult hobo spiders inside homes; in both cases the observers expressed amazement, not only in the fact that such a small spider would attack the larger hobo, but in the efficiency of the event.

Two species of Platycryptus jumping spiders, P. californicus and P. undatus are also found within the North American range of the hobo spider. Platycryptus spp. frequent buildings and fences, and often enter houses, in much the same fashion as does Salticus scenicus. Platycryptus jumping spiders are somewhat larger (9-13 mm) than Salticus scenicus, but are behaviorally similar. While no confirmative reports of Platycryptus attacks on hobo spiders have thus far been recorded, it is probable that they do occur.

Jumping spiders of the genus Phidippus are found in various parts of the North American range of the hobo spider. Phidippus are larger than most other salticid spiders, and are capable predators. In southern Idaho and northern Utah, the most important of these in a predatory sense is the daring or "three spot" jumping spider, Phidippus audax (pictured at right). Phidippus audax is a moderately large (13-15 mm) jumping spider which has been observed to attack and kill hobo spiders on frequent occasions. Each year Eagle Rock Research receives several reports of audax engagements with hobo spiders, all ending rapidly in favor of the jumping spider. Interestingly, the presence of P. audax in the Snake River Valley of Idaho may be the result of a fairly recent range extension for this arachnid: This species is generally considered to be found east of the Rocky Mountains (although at least two specimens have been recorded as far west as Washington State). In 1983, during field investigations to determine the presence of spider species in Bonneville County, Idaho, only one specimen of P. audax was discovered: Since that time the numbers of these spiders found or submitted from that same area has increased from year to year. Phidippus audax is now commonly found in and around human dwellings in the Idaho cities of Blackfoot, Boise, Idaho Falls and Pocatello.

Several additional species of Phidippus are found within the North American range of the hobo spider. Some of these, such as P. borealis and P. clarus may occassionally interact with the hobo spider, but probably do not act as major competitors/predators due to habitat differences, diurnal vs. nocturnal schedules, and other factors. The Johnson's jumping spider, Phidippus johnsoni, is a moderately large (11-13 mm) salticid that is found beneath rocks throughout much of the hobo's North American range: This brightly colored species (brick red dorsal abdomen, with black legs and cephalothorax) is most often found in habitats quite distant from established hobo spider populations, but it has been found in urban areas close to hobo spider populations in southern Idaho. P. johnsoni definitely competes with the hobo spider for food to some degree, and may occasionally take hobo spiders as prey. Interestingly, P. johnsoni has itself been occasionally implicated in biting humans, but none of these cases have been serious. The largest jumping spider found within the North American range of the hobo spider is Phidippus octopunctatus (pictured at left). Large octopunctatus specimens may approach 25 mm in body length, are gray to brownish-gray in color, and at first glimpse may be momentarily mistaken for a small mouse. While this species is absent from much of the North American range of the hobo spider, it does have a spotty distribution in northern areas of the Great Basin Desert within the hobo spider's range. One Bonneville County, Idaho, population of octopunctatus resides in the same area as a major population of hobo spiders: This situation produces an ideal environment for food competition, as well as predation by P. octopunctatus on hobo spiders.

Several other genera of jumping spiders reside within the North American range of the hobo spider. Most of these are smaller species, and most of them do not live in habitats currently occupied by established hobo spider populations. It can be expected that these genera do compete for food to a small degree, and may in certain circumstances prey upon hobo spiders. Jumping spiders as a group may be considered as harmless, beneficial arachnids, which possess unique characteristics, setting them apart from other arthropod species. Persons interested in further pursuing information on jumping spiders will find additional links on our Other Interesting Sites page.

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