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Scientists think that the Asian tiger mosquito -- one of two mosquitoes that carries Zika, dengue, and yellow fever -- first arrived in Texas in shipments of used tires in 1987. Since then, they've spread inexorably across the country.

Why they matter: The Aedes aegypti mosquito gets all the fame because it almost exclusively feeds on humans, lives in urban areas and is an effective vector for Zika and a number of other diseases. The Asian tiger mosquito (Aedes albopictus) — prefers less populated areas and is as likely to bite humans as animals, but it carries many of the same diseases and is a more effective breeder. Unlike aegypti, which can't survive harsh northern winters, albopictus has overwintered as far north as Connecticut. There are concerns that range will expand with climate change.

Expand chart

Data: Reported Distribution of Aedes ( Stegomyia ) aegypti and Aedes ( Stegomyia ) albopictus in the United States, 1995-2016; Map: Lazaro Gamio / Axios

What the map shows: Each highlighted county represents a place where at least one Asian tiger mosquito was sighted. However, many counties lack mosquito control and surveillance programs, and federal funding for mosquito research has been scaled back since the mid-2000's. It's likely the map underestimates the insect's distribution.

What it doesn't show: Where the mosquitoes are right now. In many of these locations, the blood-suckers may have been introduced and then died off. It doesn't mean a breeding population was established, but it does show their spread.

How they spread: Aedes mosquitoes are particularly well-adapted to life alongside humanity. They evolved to breed in the notches and holes in trees, but they've adapted to the nooks and crannies we leave scattered around our homes and cities. They lay their eggs on the sides of containers next to tiny pools of water, and their eggs can survive dried out for months. If that container is moved, so is a generation of mosquito.

Hijacking humans: Many areas, like California and Arizona, are too dry to support mosquitoes. But humans place birdbaths and water lawns; they build swimming pools and fountains. Populations of albopictus and aegypti are established in both states.

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Why it matters: Some Democrats, including Sens. Tim Kaine (D-Va.) and Chris Murphy (D-Conn.) and Rep. Ro Khanna (D-Calif.), have criticized the Biden administration for the strike and demanded a briefing.

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Illustration: Annelise Capossela/Axios