Invasive species are sometimes less susceptible to natural enemies compared to native species, but the mechanism is often unclear. Here we tested two potential mechanisms for lower parasitism of invasive species: density-dependent parasitism and preference for human-dominated habitats. We investigated how variation in host density and habitat type affect egg sac parasitism in two widow spider species (family Theridiidae). We compared parasitism on the egg sac of the brown widow, Latrodectus geometricus, an urban invasive species, and the white widow, Latrodectus pallidus, a species native to Israel. To investigate variation in host and parasitoid density, we measured nearest-neighbor distance between spider webs and parasitism rates in 16 sites, and in a single site monthly throughout a year. In L. pallidus, denser sites were more heavily parasitized (up to 55%) and parasitism rate increased with population density throughout the season. Extremely dense L. geometricus populations, however, had very low rates of parasitism (0-5%). We then conducted an egg sac transplant experiment in human-dominated and natural habitats. We found no parasitism of either species in the human-dominated habitat, compared to 30% parasitism of both species in the natural habitat. In addition, we found evidence for higher predation of L. pallidus than of L. geometricus egg sacs, particularly in the natural habitat. These combined results suggest that the human-dominated habitats inhabited by L. geometricus have a lower abundance of predators and parasites. We conclude that lower parasitism and predation in human-dominated habitats could contribute to the invasion success of L. geometricus.

Redback spider (RBS) antivenom (RBSAV) use appears to have decreased since the results of the RAVE-2 antivenom efficacy study were released. The aims of this study were to assess change in RBSAV use over time and compare responses to treatment for antivenom and other analgesics.
Retrospective audit of RBS bite referrals to a toxicology unit, from January 2010 to January 2022. Data included demographics, pain severity, treatment (analgesia or RBSAV), response to treatment, re-presentation rate, adverse events, change in antivenom use over time.
Of 270 presentations, 157 with moderate or severe pain were included (RBSAV n = 51, analgesia n = 106). Median age was 39 years, n = 81 (51%) female. Those receiving antivenom were more likely to report severe pain n = 46/51 (84%) versus n = 68/106 (58%) (P = 0.006). Eighty-three percent of antivenom doses were administered between 2010 and 2013. Analgesia-only group received various combinations of paracetamol, NSAIDs, and opioids. In those receiving RBSAV, 17/48 (35%), 26/48 (54%), 5/48 (10%) reported a partial, complete or no reduction in pain, respectively, versus 30/77 (39%), 43/77 (58%) and 4/77 (5%), for analgesia-only group. Post-treatment pain was not recorded in three RBSAV and 28 analgesia-only patients. Pain reduction was no different for intravenous and intramuscular antivenom. Re-presentation for ongoing pain was more common in the analgesia-only group, 16/106 (15%) versus 1/51 (2%) for antivenom (P = 0.013).
Antivenom use fell over the study period. There was no difference in pain relief between RBSAV and analgesia-only groups. RBSAV, regardless of route of administration, was no better than standard analgesics in pain reduction in the present study.

Black widow spiders (Latrodectus sp.) are distributed worldwide, and in Albania the L. tredecimguttatus Rossi, 1790 has been the dominant spider. Other medically important spiders in Albania include the brown recluse with symptoms known as loxoscelism, the false black widow and the egg sac spiders; the last two inducing similar symptoms to a wasp sting.
METHODS: The data analyzed is from a decade-long study of 125 patients hospitalized in the regional hospital of Fier County, in the Western Lowland of Albania from May 2009 and to October 2018.
OBJECTIVE: Although the venom is rarely fatal, the recent spider bites raise questions about the influence of higher air temperatures on their possibly increased toxicity.
RESULTS: Significantly the severity of the α-latrotoxin rises during the summer, when human-spider contact frequency is higher and when the black widow spiders have an increased motivation to protect their egg sacs.
CONCLUSIONS: This study revealed an increased severity of the black widow bites with respect to patient health, shown via all the severe systemic symptoms, during those months with higher temperatures.

Humankind has always been fascinated by venomous animals, as their toxic substances have transformed them into symbols of power and mystery. Over the centuries, researchers have been trying to understand animal venoms, unveiling intricate mixtures of molecules and their biological effects. Among venomous animals, Latrodectus Walckenaer, 1805 (widow spiders) have become feared in many cultures worldwide due to their extremely neurotoxic venom. The Latrodectus genus encompasses 32 species broadly spread around the globe, 14 of which occur in the Americas. Despite the high number of species found in the New World, the knowledge on these spiders is still scarce. This review covers the general knowledge on Latrodectus spp. from the Americas. We address widow spiders\' taxonomy; geographical distribution and epidemiology; symptoms and treatments of envenomation (latrodectism); venom collection, experimental studies, proteome and transcriptome; and biotechnological studies on these Latrodectus spp. Moreover, we discuss the main challenges and limitations faced by researchers when trying to comprehend this neglected group of medically important spiders. We expect this review to help overcome the lack of information regarding widow spiders in the New World.

Risks of sociality, including competition and conspecific aggression, are particularly pronounced in venomous invertebrates such as arachnids. Spiders show a wide range of sociality, with differing levels of cannibalism and other types of social aggression. To have the greatest chance of surviving interactions with conspecifics, spiders must learn to assess and respond to risk. One of the major ways risk assessment is studied in spiders is via venom metering, in which spiders choose how much venom to use based on prey and predator characteristics. While venom metering in response to prey acquisition and predator defense is well-studied, less is known about its use in conspecific interactions. Here we argue that due to the wide range of both sociality and venom found in spiders, they are poised to be an excellent system for testing questions regarding whether and how venom use relates to the evolution of social behavior and, in return, whether social behavior influences venom use and evolution. We focus primarily on the widow spiders, Latrodectus, as a strong model for testing these hypotheses. Given that successful responses to risk are vital for maintaining sociality, comparative analysis of spider taxa in which venom metering and sociality vary can provide valuable insights into the evolution and maintenance of social behavior under risk.

Black widow spiders (Latrodectus spp.) are generally perceived as inhabiting southern or western United States. However, some species, such as the northern black widow, Latrodectus variolus, are also found in more temperate regions of USA and adjacent Canada. This species also appears to expand its range northward with the climate change increasing the risk of human encounters. To our knowledge, this is the first case report of a pediatric envenomation from a northern black widow bite in northeastern US. Medical practitioners often fail to recognize the signs and symptoms of latrodectism delaying effective treatment. Even in more northern locales, healthcare workers should take black widow spider envenomation under consideration in the differential diagnosis particularly with suspected exposure.

BACKGROUND: Latrodectism is a rare, but potentially severe, clinical syndrome caused by spider of the genus Latrodectus. L. tredecimguttatus is widespread in Italy and its bite cause the injection of α-latrotoxin that cause depletion of acetylcholine at motor nerve endings and release of catecholamines at adrenergic nerve endings. We describe the first clinical case of L. tredecimguttatus poisoning successfully treated with L. mactans antivenom from North America.
METHODS: A healthy 60-year-old patient was admitted to the emergency department after unknown insect sting or arachnid/snake bite. In the early morning, the patient was working in the countryside when he felt a sting-like pain in the medial area of the right lower leg, associated with an intense burning sensation. An hour later he developed agitation, hoarseness, sweating, abdominal distress and intense pain in his right leg. In the emergency room vital signs showed a hypertensive crisis, tachycardia and peripheral oxygen desaturation. ECG was normal and ABE showed mixed acid-base disorder. Blood tests showed leukocytosis with neutrophilia, high levels of myoglobin, with normal coagulation and normal plasmatic cholinesterase. Neck, thorax and abdomen CT scan, with and without contrast medium, was negative. Four hours after admission hypertension worsened with board like rigid abdomen and onset of fasciculations, tremors, miosis and intense regional sweating. The definitive diagnosis of poisoning by L tredecimguttatus was based on the clinical picture. Within short time the antidote was provided by the Poison Centre and administered. A marked improvement of the symptomatology was noted after 30 minutes, and 1 hour later all symptoms were under control. The patient was discharged after 2 days.
CONCLUSIONS: The clinical presentation of a patient suffering from latrodectism places the clinician in front of a challenging differential diagnosis. Following the suspicion, the first-line doctor is invited to discuss the case with a toxicologist, in order to confirm or exclude the diagnosis and implement all therapeutic measures. In our clinical case, the absence of organic lesions, laboratory tests not suggestive for other causes, and the presence of typical clinical feature suggested the diagnosis of L tredecimguttatus poisoning. This hypothesis was then supported by the close temporal relation between antivenom administration and symptoms improvement. With this case, we report the first use of L mactans antivenom from North America to treat L.tredecimguttatus poisoning and we confirm its effectiveness in counteracting latrodectism caused by this spider.

BACKGROUND: Black widow spider (Latrodectus spp) envenomation represents the most medically significant spider envenomation in the United States, prompting more than 2500 calls to poison centers annually. The female spider, which is responsible for symptomatic envenomations, is classically described as a shiny black spider with a red hourglass-shaped marking on the ventral abdomen. Clinical features of envenomation include painful muscle cramping, abdominal pain, and autonomic disturbances, such as tachycardia, hypertension, and diaphoresis. \"Latrodectus facies\" or \"facies latrodectismica\" is an additional distinctive but rarely described clinical finding characterized by periorbital edema, lacrimation, and blepharospasm.
METHODS: A 6-year-old female developed the typical clinical features of Latrodectus envenomation after being found in bed with a Western black widow spider (Latrodectus hesperus) with no ventral marking. She initially improved with opioid analgesia, but 6 h later her symptoms worsened again, and concurrent with this worsening she developed Latrodectus facies. She received additional opioid analgesia and all her symptoms resolved within 24 h. Her mother provided informed and written consent for the acquisition and publication of the facial photographs presented. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: A high degree of clinical suspicion is necessary to correctly diagnose Latrodectus envenomation, especially when the spider escapes unnoticed or in young children in whom the bite is not witnessed. To our knowledge, Latrodectus facies has not been reported previously in a young child, and recognition of this finding will aid clinicians in limiting unnecessary interventions and administering appropriate therapy.

Temperature strongly influences the physiology and behavior of ectotherms. Persistence within different environments can be limited by thermal tolerances. These thermal tolerances can also shift through life stages and differ between sexes. The critical thermal maximum (CTMax) defines the temperature at which animals experience unorganized locomotion or spasms. In this study, we tested if CTMax varied between a native and an invasive widow species. We separately tested if CTMax varied by widow life stage and sex. We predicted that the invasive species would have higher CTMax due to originally inhabiting warmer climates. We also predicted that juveniles and male widows would possess higher CTMax because they are more mobile and could experience a greater scope of thermal extremes throughout landscapes. We did not find a difference in CTMax between the species, but we did find differences across development stages. Temperature of spasms and death decreased with developmental stages, which corresponds with previous studies in spiders. Future studies of ontogenic and interspecific comparisons will be crucial for more broadly understanding how upper tolerances shapes species persistence in changing climates or ability to invade new habitats.

BACKGROUND: Nowadays use of specific antivenin for latrodectism is considered as the most effective treatment in the world. This study was undertaken to investigate the efficacy of specific antivenom against histopathological complications caused by Latrodectus dahli venom on liver, heart and kidneys tissues within 72h.
METHODS: Two groups were selected, each one contained 6 male New Zealand rabbits weighing 2±0.5kg. The animals were anesthetized with 0.5ml ketamine and 0.5ml xylazine by intramuscular route. The L. dahli venom (0.5mg/kg) was injected subcutaneously to both the groups. The second group of rabbits 24h after the venom injection received specific antivenom by intravenous route. Seventy-two hours after the venom and antivenom injections, the rabbits were dissected to obtain heart, liver and kidney tissues. The tissues were stained by hematoxylin and eosin stains and histopathological studies were examined by optical microscope.
RESULTS: In group one, the venom induced myocytolysis, myocarditis, coagulation necrosis in the heart tissue and the liver tissue showed central vein congestion, congested vessels, dilated sinusoids and inflammation. However, no significant histopathological complications were observed in kidney tissues. In the second group, antivenom injection greatly prevented escalation of the complications on foresaid tissues.
CONCLUSIONS: Latrodectus dahli venom induces histopathological complications on vital organs. Specific antivenom injection, 24h after the venom injection, could protect the tissues from incidence and intensification of histopathological complications. Future studies in human beings should be conducted to assess the protection against the specific-Latrodectus antivenin.