Alder leaf beetle vs Cobweb weaver

Agelastica alni compared with Steatoda nobilis

Key Differences

• Alder leaf beetle is Least Concern while Cobweb weaver is Not Evaluated.

Taxonomic Classification

Rank	Alder leaf beetle	Cobweb weaver
Kingdom same	Animalia (Animals)	Animalia (Animals)
Phylum same	Arthropoda (Arthropods)	Arthropoda (Arthropods)
Class	Insecta (Insects)	Arachnida (Arachnids)
Order	Coleoptera (Beetles)	Araneae (Araneae)
Family	Chrysomelidae	Theridiidae
Genus	Agelastica	Steatoda
Species	Agelastica alni	Steatoda nobilis

Evolutionary Relationship

Alder leaf beetle and Cobweb weaver share a common ancestor at the Phylum level: Arthropoda. (Arthropods)

Conservation Status

Alder leaf beetle

LC — Least Concern

Cobweb weaver

NE — Not Evaluated

Physical Characteristics

Attribute	Alder leaf beetle	Cobweb weaver
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

Alder leaf beetle

Habitat

Typically found in virtually all terrestrial and freshwater habitats.

Range

Distributed across Belgium, Denmark, Norway, Sweden, and United States.

Cobweb weaver

Habitat

Typically found in terrestrial habitats from forests to deserts.

Range

Widely distributed across Europe (7 countries), North America (United States), and South America (Ecuador).

Alder leaf beetle

The Alder leaf beetle (Agelastica alni) is a species in the genus Agelastica. It is currently classified as Least Concern on the IUCN Red List. Typically found in virtually all terrestrial and freshwater habitats.

Cobweb weaver

The noble false widow (Steatoda nobilis) is a theridiid spider that has attracted considerable media attention in the British Isles and along the Atlantic coast of Europe due to its painful but rarely dangerous bite and its rapid range expansion facilitated by human activity. Originally native to the Canary Islands and Madeira, the species arrived in southern England during the 19th century, likely via banana shipments, and has since spread northward through Britain and westward into Ireland, while also establishing populations along the Iberian Peninsula and Atlantic France. Females are robust, with a dark brown carapace and a distinctive cream-colored pattern on the bulbous abdomen that varies between individuals; females reach 8.5–14 millimeters in body length, making this one of the larger European theridiids. The species constructs persistent, tangled cobwebs in sheltered locations outside buildings—under window ledges, in door frames, and in garden walls—as well as within homes in cooler seasons. It is a generalist predator, capturing insects and other invertebrates, and has been reported to occasionally subdue prey considerably larger than itself, including small lizards. Steatoda nobilis venom produces steatodism, which can cause localized pain, swelling, and in rare cases systemic symptoms. Its conservation status has not been formally assessed, but its expanding range demonstrates considerable resilience.

Shared Countries

Both species can be found in 3 countries:

🇧🇪 Belgium 🇩🇰 Denmark 🇺🇸 United States