ACMT Toxicology Visual Pearls: Spider Bite

Answer: D -The venom is more potent on a volume-per-volume basis than the venom of a pit viper.

Black Widow Spider Basics

Lactrodectus mactans (black widow) is one of 5 species of widow spiders found throughout the United States. They are present in every state except Alaska. The classic red hourglass-shaped ventral marking on the abdomen is specific to L. mactans. Black widow females are larger, more venomous, and more toxic than black widow males. Their webs are large, irregularly shaped, and typically found by wood piles, barns, sheds, and garages.

The venom is neurotoxic, not cytotoxic, and more potent on a volume-per-volume basis than the venom of a pit viper.¹ The major toxic component of widow venom, α-Latrotoxin, results in massive presynaptic release of several neurotransmitters, including norepinephrine, dopamine, neuropeptides, acetylcholine, glutamate, and γ-aminobutyric acid (GABA).¹

Each year, the U.S. National Poison Data System (NPDS) receives report of approximately 2,600 exposures to Lactrodectus species.² These exposures peak in late summer and early fall, however 65% are associated with only minor symptoms.²

Black Widow Spider Envenomation: Bedside Pearls

Clinical effects include:^1–3

• Severe local pain at the site of the bite (which typically migrates proximally)
• Nausea and vomiting
• Abdominal pain
• Hypertension
• Anxiety
• Diaphoresis
• Muscle cramping
• Restlessness

Pain and severe muscle cramping may mimic an acute surgical abdomen. Although symptoms usually resolve within 1-2 days, in cases of severe envenomation, they may persist for several days. Importantly, death has never been reported with isolated Lactrodectus envenomation.^1–3

Laboratory tests are generally not helpful. However, an elevated white blood cell count, lactate dehydrogenase, or creatine phosphokinase may be present.³

Management involves liberal use of benzodiazepines and opioids for muscle spasms and pain control. A review of black widow spider envenomations found that 70% of patients initially treated with both IV morphine and benzodiazepines obtained symptomatic relief without additional medications.³ Milder envenomations can be treated with NSAIDs and cold packs.

Equine derived antivenin is available and has been shown to reduce the duration of symptoms and reduce hospital length of stay.² However, availability is limited due to current manufacturing shortage. Administration appears to be relatively safe with mild to moderate adverse effects occurring in only a small percentage of patients.^3,4 Currently, a new purified F(ab)2 fragment antivenin is undergoing clinical trials and may be a safer alternative to the currently available whole IgG antivenin.^5,6