Cyrtophora citricola

The common name for C. citricola, “tropical tent-web,” derives from Peter Forsskal's first observations. The spider was first seen in citrus trees and Forsskal described their horizontal webs as nets. [3]

Peter Forsskal discovered C. citricola in the Arabian Peninsula posthumously naming it Aranea citricola in 1775.[3] It was classified in the Araneidae family because it creates orb-webs.[2] Between 1776 and 1864 the spider was classified under the genus Epeira, another synonym for Aranea, more commonly known as Araneus. The spider was later moved from the genus Aranea genus to Cyrtophora by Eugene Simon in 1864. This decision was made because C. citricola orb webs differ from those constructed by the genus Aranea.[4] C. citricola webs are horizontal and tent-shaped which are similar to other spider's webs in the genus Cyrtophora. Like others in the Cyrtophora family, C. citricola's 2nd, 3rd, and 4th legs have a shorter combined patella and tibia length than femurs within the same legs. Additionally, it shares the same bent-back eye pattern: a typical family defining trait. C. citricola differ from the Manogea genus of orb-web spiders due to its broader cephalic structures.

Cyrtophora citricola abessinensis was one subspecies under C. citricola that was later discovered to be a holotype in 1944.[5]

Cyrtophora citricola is a medium brown color, however, there are darker brown spots on the abdomen. In Florida male spiders are black, while females vary in their coloring and can camouflage in their webs. The females have white trichobothria. In Turkey, they usually appear brown with grey hair. C. citricola has a distinctive horizontal bifurcation at the posterior abdomen.[7][8] C. citricola is different from its other relatives because it has two pairs of dorsal tubercles and a pair of posterior tubercles.[9] C. citricola typically has seven denticles. The opisthosoma has two dorsal pairs of protuberances and two posterior lobes.[10]

They are active from the middle of summer to the beginning of fall. Adults mate between June and September.[9]

C. citricola captures its prey in the upper section of the web. The rate of prey per capita due to web deflection is relatively low and may cause spiders to aggregate together.[2] Spiders who live in social aggregates are more efficient at capturing prey than solitary spiders.[2][8]

The process of prey capturing includes multiple steps. The first step is either biting the prey or wrapping it in silk. The second step is pulling and cutting the prey out of the web. The third step is transporting the prey to the hub of the web by either carrying it in its jaws or rewrapping it and carrying it in silk. The fourth step is feeding on the prey in the hub of the web.[14]

C. citriciola has four attack sequences. In the first variation, the spider wraps its prey and bites it. After biting the prey, the spider removes the prey from the web, rewraps it, and transports it to the hub. The second sequence follows the steps of the first variation but skips the biting stage. The third variation starts with the spider biting its prey and wrapping its prey. Later, the prey is removed and rewrapped before being transported to the web hub. The fourth sequence involves spiders biting and pulling or cutting the prey. The prey is transported to the hub in the spider's jaws. Whether the prey is bitten, wrapped, or both is determined by the type of prey that is captured.[14]

C. citricola preys on moths and flies. These insects are bitten and carried to the hub on silk. Orthopteras are captured eaten by C. citricola using a variety of sequences in its captures. Other common prey include dragonflies, beetles, and pentatomids.[14]

Cyrtophora citricola is found in Asia, Africa, Australia, Costa Rica, Hispaniola, Colombia, and Southern Europe.[1] It is unable to survive in temperature below -1°C.[8][15] It was also discovered in Florida in 2000. In Florida, C. citricola makes its webs on canal bridges from the east end of Everglades National Park to the east coast. The spider lives in a wide range of environments, but it is most prevalent in olive orchards and undergrowth.[9] C. citricola is also found in tropical agricultural operations.[1]

C. citricola can be found globally unlike its close relatives that are concentrated in specific parts of the world. C. citricola's global presence may be a problem as seen in the Americas.[16] The spider is becoming common in agricultural and urban spaces. It is damaging farm operations. Currently, there are active efforts to remove the spider as its web is known to damage flora.[7]

Cyrtophora citricola exhibits thermoregulative behaviors. This trait is common in web-building spiders, including Nephila clavipes, N. maculata, and Frontinella communis. During the hottest portions of the day, the spider will position themselves so that as little surface area of their body is shown to the sun as possible.[14]

Cyrtophora citricola exhibits territorial behavior over its orb-webs. But tent webs are communal and no aggressive behavior was documented between spiders that travel across these webs. At night there are conflicts between orbless spiders and orb-possessing spiders. These fights occur due to competition for better feeding locations. Larger spiders are typically win in fights over smaller spiders.[11] Invading spiders may come from the colony's periphery, where costs to build webs are often high due to continuous repair and diminished prey capture. Peripheral webs often experience damage from weather and predators whereas central webs remain undisturbed.[2] Conflict arises when an orbless intruder approaches and vibrates the web. This action is a sign of attack and solicits the same response from the defending spider. The vibrations between the attacker and the defender continue for a few minutes. However, the invader rarely captures the web and retreats.[2]

C. citricola in Gorongosa National Park[17]

Adult male spiders look for females.[18] These spiders exhibit sexual cannibalism at high rates. Female spiders will often eat males after mating.[19] Females cannibalize males after most successful copulations, up to 100% of the time. Spider age and feeding state have no effect on whether the male will be cannibalized. This sexual cannibalism encourages males to be choosy when picking a female mate. Males prefer to mate younger, well-fed, and virgin females. Females are not as choosy in their male mates, but may prefer well-fed and older males. About 50% of females re-mate within ten days after their first copulation. Sexual cannibalism forces monogamy on the male spiders.[20]

The female begins the mating process. Females traditionally approach the male until they are 1cm from the male. At this point, the male advances quickly towards the female and tries to insert his pedipalp. If successful, copulation begins and lasts for a few seconds. This is the stage at which copulation most often fails.[20]

The male Cyrtophora citricola does not somersault into the female's chelicerae, a maneuver which is common in other cannibalizing spiders. The female bends her cephalothorax and orients herself to attack the male's abdomen while the pedipalp is in the female. The male is eaten and the pedipalp is detached from the female.[20]

The egg sacs of Cyrtophora citricola have a diameter ranging from 12-20mm. These egg sacs are laid in chains of up to 10 sacs in a row on the webs. The eggs are colored bluish- green. Each egg sac contains between 100 and 200 eggs. The eggs are shaped as flat ellipticals.[8][20] The number of eggs produced depends on various environmental factors, including food availability. Solitary females can produce up to 20% more eggs than females living in colonies.[1] The reduction of eggs in colonies may be due to better parasite protectoin and reduced predation.[20] Females with egg sacs will typically rest directly underneath the egg sac in order to guard them.[14]

Juveniles usually disperse or build their own webs off the maternal webs after four days.[21] Juveniles in larger webs are less likely to leave their mother's web. Mothers feed offspring, but when prey is scarce there is increased sibling aggression. These resource-poor conditions increase the likelihood of early dispersal from the maternal web.[21]

C. citricola prefers to select nest sites and create webs in the forks between branches and leaves.[22]

Cyrtophora citricola may exhibit aggregate social interactions with one another and live cooperatively in groups.[1] This behavior is distinct amongst spiders, as most spiders are solitary.[23] C. citricola make their own individual webs, but these individuals webs are interconnected. The large network of webs with neighboring spiders creates a massive web matrix. Given the large size and visibility of the colonial web, prey who are visually acute may avoiding approaching the colony.[23] If one member of a colonial group senses a nearby predator or prey, they perform a knee jerk on the web. This jerk often begins a chain reaction; up to 75% of nearby spiders may follow suit and jerk their webs as well.[23] Within colonies, there are three zones where spiders may live: the outside, the intermediate, and the inside zones. Spiders living in the intermediate zone have the best rates of prey capture.[1] Larger colonies have higher prey capture rates than smaller colonies do. Spiders in colonies capture prey at higher rates at night compared to day.[23]

C. citricola generally coexist peacefully. They may exhibit aggressive behaviors if another spider tries to take their prey.[8] [20][24] Colony living may have evolved because of the foraging benefits of group living for the spiders. Solitary living may be favored when prey is scarce. Conditional sociality is another evolutionary explanation for why group living evolved in this species.[11] One possibility may be protection against parasites or predators. Another possibility is that colonial webs allow juveniles to easily create their first webs.[1]

Some C. citricola live solitarily, alone without other organisms. Solitary spiders have larger webs, produce more eggs, and have more kleptoparasites than colonies. There is no difference in female size and prey capture when comparing colonial and solitary spiders. There are two hypotheses for the limited physical differences between solitary and colonial spiders. The first hypothesis is that spiders can move back and forth between colonial and solitary living throughout their lives. The second hypothesis is that prey capture is similar in both colonial and solitary spiders, allowing for similar physical development. Both hypotheses may explain the many similarities between solitary and colonial spiders.[1]

Argyrodes argyrodes, another species of spider, may steal Cyrtophora citricola's prey and eggs.[8] [25][26] In addition, Holocnemus pluchei, also known as daddy long-legs, has been found to build their webs off of C. citricola's webs. Holocnemus pluchei exhibit aggressive behavior towards C. citricola and are observed eating C. citricola juveniles.[1] C. citricola will drop to the ground if attacked, in an attempt to camouflage.[18] C. citricola may also pull all of its legs inwards towards its abdomen.[14]

Argyrodes gibbosus often acts as a kleptoparasite to C. citricola, stealing prey that the C. citricola caught.[1] Argyrodes gibbosus is known to switch strategies depending on where the host is located. Prey is stolen when the host is in the hub of the web. Argyrodes gibbosus was seen waiting for the C. citricola to go foraging before consuming their eggs.[27]

Pediobius pyrgo is a type of wasp that lays its eggs in C. citricola egg sacs. The wasp is present in the Iberian Peninsula and in the Canary Islands.[28] Philolema palanichamyi is another type of wasp that lays its eggs in C. citricola egg sacs. The wasp affects these spiders primarily in the Canary Islands and can parasitize around 40% of egg sacs. Wasp larvae feed on the spider's eggs and each larva will devour significant portions of the egg sacs. The incubation takes approximately seven weeks. Wasp larvae often cause a large portion of parasitized spider egg-sacs to die. Parasitization approximately decreases emerging spiderling populations by 60%.[28]

Ornamental trees, fruit trees, and various flowering plants in the genus Eugenia including Eugenia coronata, have high concentrations of Cyrtophora citricola. These plants and trees may experience incomplete death when C. citricola's webs span over their leaves.[7][8] This may be due to the thickness of the webs that can restrict airflow to the leaves. As a result, some authorities have opted to use high-pressure water sprayers and chemical controls to exterminate colonies.[29]

C. citricola is problematic for many agricultural operations in South American including coffee and citrus plantations. It is listed as an important agricultural pest in the Dominican Republic due to its devastating impact on citrus trees.[30] Additionally, it is increasingly common in the Southern states of North America. In Florida, the spider has become a common backyard nuisance.[28]

Sources

• Álvares, É.S.S. & De Maria, M. (2004). First record of Cyrtophora citricola (Forskål) in Brazil (Araneae, Araneidae). Revista Brasileira de Zoologia 21(1):155-156 PDF doi:10.1590/S0101-81752004000100026
• Edwards, G.B. (2012): Cyrtophora citricola (Araneae: Araneidae), a Colonial Tentweb Orbweaver Established in Florida. DPI Entomology Circular 411:. PDF
• Platnick, Norman I. (2009): The world spider catalog, version 10.0. American Museum of Natural History.

Wikimedia Commons has media related to Cyrtophora.

• Pictures of C. citricola
• Pictures and information on C. citricola from Portugal
• Cyrtophora citricola on the UF / IFAS Featured Creatures website.