Tylorida ventralis (Thorell, 1877)

Big-bellied Tylorida Spider

横 带 隆 背 蛛

Introduction

Tylorida ventralis (Thorell, 1877) belongs to the family Tetragnathidae. They are long-jawed orb weavers with long legs because they have a distinctive cherlicerae that are long and wide, and their webs are shaped delicately like an orb with open hubs. Under the genus Tylorida Simon, 1894, they can be easily distinguished from other genera of the sub-family Leucauginae from their first pair of legs, which are longer than their second pair by a ratio of more than 1.6.

Contrary to common beliefs that female spiders are cannibalistic and reluctant to participate in sex, the sexual behaviour in T. ventralis offered a complete twist to this notion, making them one of the “horniest” spiders.

Biology

Unusual sex in T. ventralis

Tylorida ventralis mating pair (male: left, female: right) (Photo taken by Nicky Bay (C))

Copulation in all spiders with the exception of the harvestman (Order: Opiliones) occurs indirectly through a process called sperm induction. This process involves the transference of semen from the genitalia at the ventral side of its abdomen into its palps situated in front of its head first, before inserting the palp into the epigynum of the female located at the ventral side of the abdomen.

Male (left) flexing his palp on the chelicera and approaching the female (right). (Photo taken by Nicky Bay (C))

Copulation in T. ventralis usually occurs within the female's orb-web where the male will approach the female in the web and flexes his palps in a rotatory manner, which is normally a prelude to sperm induction and copulation. Contrary to the conventional notion that female spiders are reluctant or passive in sexual advances by the males and is extremely aggressive or even cannibalistic towards their partners, a study by Mafham and Cahill

A male (left) T. ventralis trying to insert the palp into the female's epigynum (right). (Photo taken by Nicky Bay (C))

Moreover, insertion of the palp (containing the sperms) into the epigynum in T. ventraliscan be repeated hundreds of times during the mating period which can last for as long as 10 hours.

Palp being inserted into epigynum (Male = right, Female = left). (Photo taken by Nicky Bay (C))

There are two possible explanations for this bizarre copulation behaviour inT. ventralis. Firstly, this behaviour seems to constitute an unusual form of mate-guarding and will prevent any further insemination by other males, thus confering higher sperm priority. Secondly, by staying in the web longer, the male derives benefits by stealing a proportion of the food meant for ovarian maturation by the female. At the same time, the female also benefits from the extended copulation by reducing the risk of predation or capture (50% reduction).

After insemination, the female is able to retain the sperm mass outside of the uterus in a specialized structure (spermathecae) until the eggs are ready for fertilization.
Thus, they are able to lay several batches of eggs. She will then protect the eggs by spinning a soft layer of fine yellow silk (Tubiliform silk) as shown in the photo below. In most cases, the mother will care for the offsprings and actively secure food for her brood until they hatch.

Egg sac of T. ventralis (Photo by Rayson Lim (C))

Physiology of feeding and digestion

Digestion of their prey occurs externally where once the prey has been subdued via wrapping them with silk, it will cut and mash the prey with its cheliceral teeth and pour in enzymes derived from the front end of the alimentary canal. Once the internal organs of the prey starts to liquify, it will be sucked out and more enzymes will be introduced until the internal contents have been fully digested and consumed. The liquified content will then be ingested into the midgut due to the action of the sucking stomach. Any remaining particulate solids will be filtered out through the bristles around the mouth as well as by a filter system in the throat. The final stages of the digestion and adsorption of food occur in the midgut.

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Distribution

Habitat

Countries: India; Sri Lanka; Southern China; Taiwan; Japan; Papua New Guinea; Myanmar; Laos; Malaysia; Singapore; Indonesia

Map showing the distribution of T. ventralis (Orange parts indicate presence of T.ventralis). The distribution is based on the information of examined specimen by various authors as shown in Table 1.

Description locality and specimen information

Table 1 shows the information of collected specimens in various locality.

Abbreviations
ZSI - Zoological Survey of India
RMNH - Rijksmuseum van Natuurlijke Historie, Leiden
ZMH - Zoologisches Museum Hamburg
ZMK - Zoologiske Museum København
RMBR - Raffles Museum of Biodiversity Research
ZRC - Zoological Reference Collection
SMF - Research Institute Senckenberg, Frankfurt am Main, Germany
NSMT - National Science Museum, Tokyo

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Etymology

Synonyms

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Diagnosis

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Description

Anatomical terms

Illustrated anatomical terms (Rayson (C))

Sexual dimorphism

Male and female are similar in shape, colour and ocular area arrangement with the exception of:
1) Size (♂: 5.49~6.21mm, is slightly smaller than ♀: 6.75~7.38mm).
2) Legs of males are longer and thinner than females.
3) Promargin of chelicera with 3 teeth (♀ & ♂) but retromargin has 4 - 5 teeth (♀) and 4 teeth (♂).

Cephalothorax

Literature and references

Discussion area

This page was authored by Lavaniya Ilangoby Lim Bock Hing Rayson
Last curated on 30 July 2020in 2011