Spitting spider genus Dictis recorded in the Caucasus for the first time

Deep in the semideserts of eastern Georgia, a tiny spider has just rewritten the arachnological map of the Caucasus. Researchers report the first record of the spitting spider genus Dictis in the region, after a field expedition to Vashlovani National Park turned up a female carrying an egg sac under rocks near the village of Mijniskure. The find, published in the journal Caucasiana, is more than a simple range extension: it comes with a formal taxonomic reshuffle, transferring a poorly studied species from the genus Scytodes to Dictis, and it delivers the first-ever drawings of the species’ internal female genitalia, structures that taxonomists rely on to tell closely related spitting spiders apart.

Spitting spiders, the family Scytodidae, are among the strangest hunters in the spider world. Rather than chasing prey or building webs, they stalk soft-bodied insects and squirt a sticky, venom-laced spray from openings near their fangs, gluing the victim to the ground before feeding at leisure. The family is relatively small, with over 250 extant species in four genera, and it is most diversified in tropical and subtropical regions. Several members are considered cosmopolitan, synanthropic species that thrive alongside humans. Until now, the Caucasus was thought to host just a single widely distributed representative of the family, Scytodes thoracica, absent only from the mountain regions.

That scarcity always looked suspicious. Neighboring Turkey and Iran harbor noticeably richer spitting spider faunas, which suggested that the Caucasus had simply been underexplored. Recent fieldwork partially confirmed this hunch: an expedition to Vashlovani National Park had already yielded six spider species new to the Caucasus from different families, including two described as new to science. The new study builds on that momentum, presenting the first Caucasian record of Dictis based on a female with an egg sac collected during a trip to the park, together with two adult males reared in captivity from that very egg sac.

The taxonomic centerpiece of the paper is a new combination. The species formerly known as Scytodes strandi, described by Spassky in 1941, is now transferred to the genus Dictis as Dictis strandi comb. nov. The transfer rests on careful examination of the collected female and the two males raised to maturity from the egg sac. Dictis strandi belongs to a genus whose type species, Dictis striatipes, was described by Ludwig Carl Christian Koch back in 1872. Distinguishing the two species required a close look at minute genital structures: males of D. strandi differ from the polymorphic D. striatipes by having a straight retrolateral subapical process located at the base of the psembolic apex, roughly 4.3 times shorter than the psembolus, whereas D. striatipes bears a prolateral pick in that position.

Females tell a parallel story. The female of D. strandi can be separated from D. striatipes by an oval receptacle head and a thinner receptacle stem in the endogyne, the internal female genital apparatus, in contrast to the rounded receptacle head and thicker stem of its congener. The postepigastric fovea and positioning ridges, two sets of cuticular landmarks on the ventral abdomen, are separated from each other by about three times their width in D. strandi, versus four times in D. striatipes. The endogyne of D. strandi is depicted for the first time in the new paper, a milestone for a species that had remained poorly studied since its original description more than eight decades ago.

The redescription documents both sexes in detail. Adult males measure about 4.73 to 4.75 millimeters in total length, with a carapace roughly 2.65 millimeters long and 2.31 millimeters wide. The female is dramatically larger, at 9.87 millimeters total length, with a carapace 3.97 millimeters long and 3.47 millimeters wide. Both sexes share a beige-light yellow carapace ornamented with two broad longitudinal light-brown bands running from the clypeus to the posterior part of the carapace, along with broken lateral bands of lines and spots. The abdomen carries three pairs of large dark spots forming longitudinal bands dorsally, and the female’s legs are far more boldly patterned, with dark-brown femora, patellae, and tibiae on the first two leg pairs and annulated segments on legs III and IV.

Leg proportions, a standard taxonomic character in spiders, are recorded for both sexes as sums of femur, patella, tibia, metatarsus, and tarsus lengths. In males, leg I reaches about 13.23 millimeters, by far the longest, followed by leg IV at roughly 9.91 millimeters, leg II at 9.12 millimeters, and leg III at 7.44 millimeters. The female shows a similar hierarchy, with leg I at 13.37 millimeters, leg IV at 12.81 millimeters, leg II at 12.24 millimeters, and leg III at 10.76 millimeters. These elongated first legs are typical of spitting spiders, whose long, slender limbs and oversized anterior lateral eyes give them a distinctive, almost giraffe-like silhouette under magnification.

The laboratory work behind the discovery reads like a miniature husbandry saga. The live female was placed in a 10 milliliter vial without substrate and was found dead on 1 July. A carefully opened egg sac revealed four fully developed spiderlings, of which only two molted successfully and were transferred to separate 5 milliliter vials. The juveniles were fed daily with soft-bodied arthropods, including Collembola, Thysanura, and Drosophila species, and reached sexual maturity about two and a half months later, in the first decade of September. Intriguingly, the adult males refused to eat once mature. These observations suggest an annual life cycle for the species, a useful natural-history data point for a spider whose biology had been essentially undocumented.

Field and imaging methods were equally meticulous. Elevations and GPS coordinates were logged with a Garmin GPSMAP 64s receiver, and the specimens were preserved in 96 percent ethanol and stored in a freezer at minus 22 degrees Celsius in the scientific collections of Ilia State University in Tbilisi. Specimens were examined with a Zeiss Stemi 508 stereo microscope fitted with an 8:1 zoom and a front lens, and diagnostic drawings of the left male palp and the endogyne were made from microscope photographs using a graphics tablet. The epigyne and endogyne were cleared in a 30 percent potassium hydroxide solution before study. Live specimens were photographed with a Canon EOS 90D and a 60 millimeter macro lens, while preserved material was imaged with a Canon EOS 5D Mark II and an MP-E 65 millimeter macro photo lens, with final images prepared using focus-stacking software.

The geographic implications are striking. Dictis strandi was previously known from Iran and Central Asia, with the exception of Kazakhstan, and the Georgian record now stands as the westernmost occurrence of the entire genus. The new material was collected in the semidesert of Vashlovani National Park in Kakheti, under rocks, at coordinates of about 41.12 degrees north and 46.65 degrees east. For a genus most at home in tropical and subtropical latitudes, its presence in the Caucasus semidesert hints at relict populations or unrecognized dispersal corridors bridging Central Asia and western Eurasia. With the Caucasus spitting spider fauna now shown to be richer than a single species, and with adjacent Turkey and Iran still far better surveyed, the region’s semideserts may yet conceal more taxonomic surprises waiting under the next rock.

Subject of Research: Taxonomy and biogeography of spitting spiders in the Caucasus

Article Title: The first record of Dictis L. Koch, 1872 ( Araneae , Scytodidae ) in the Caucasus

Article References: Seropian, A. (2024). The first record of Dictis L. Koch, 1872 (Araneae, Scytodidae) in the Caucasus. Caucasiana, 3, 215-221. https://doi.org/10.3897/caucasiana.3.e138762

Image Credits: AI Generated

DOI: 10.3897/caucasiana.3.e138762

Keywords: spitting spiders, Scytodidae, Dictis strandi, Caucasus, Georgia, Vashlovani National Park, taxonomy, new record, endogyne, biogeography, first, record