“Uno . . . Uno . . . ” Mariana’s voice announces mosquito release points as the van makes its way through Medellín’s neighborhoods. At every “uno,” Jairo uncovers the netting from a container of Wolbachia-infected Aedes aegypti mosquitoes and sticks his arm out of a window in the side of the van. He taps the container against the window ridge, encouraging any stragglers to take flight. We get a brief glimpse of the little cloud of mosquitoes suddenly let loose into the heat of Medellín before the van turns the next corner. Next to me, Leonardo swings an electric tennis racket to protect us from any mosquitoes that have escaped. Each victim’s death is signaled by a sharp crack and sizzle, accompanied by the smell of burnt wings.

Why release more mosquitoes? They kill millions of people every year and spread an array of debilitating diseases. With a dearth of treatment options, global health interventions commonly opt for a preventative approach that frames the mosquito as the enemy to combat—traditionally through the use of insecticides, as well as physically destroying mosquito breeding sites. Yet a different biopolitics of managing mosquitoes is being promoted by the World Mosquito Program (WMP), one that forwards the notion of coexisting with the mosquito. Indeed, across the world this Australian project is releasing Aedes aegypti mosquitoes infected with a strain of Wolbachia bacteria that significantly reduces the insect’s ability to transmit dengue, Zika, and chikungunya. Reproducing with their wild counterparts ensures the transmission of the bacteria to the mosquito’s offspring, resulting in the gradual and self-sustaining replacement of a dangerous vector with a biologically altered mosquito rendered “flying public health tool” (Beisel and Boëte 2013).

In Colombia, the WMP is intervening in Medellín, turning the city into an urban laboratory in which emerging landscapes of responsibility and care must be negotiated. For the WMP, caring for the human population involves caring for and with the mosquito as public health ally. Yet multispecies care in this particular case is challenging. Living with mosquitoes involves shifting from killing the mosquito-enemy to caring with the bacteria-infected “healthy” mosquito. The success of the WMP is premised on a reconfiguration of multispecies relations and requires labor and active engagement—from both the project workers and Medellín’s residents. However, coexisting with a mosquito reveals the ambivalences and complexities of multispecies care.

“¡Hijo de puta!” In the WMP insectary where millions of Aedes aegypti are being reared for release, Emma swats a mosquito that has found her bare skin. Here I learn the etiquette of cultivating bloodsucking critters, admiring the care the laboratory workers bestow upon the insects in cages—including feeding them human blood so that the females can obtain the protein necessary to produce eggs—while simultaneously noting how it is acceptable to kill the escaped mosquitoes that are biting us. This ambivalence is embodied in the way Emma speaks about the insects, expressing concern when she thinks the mosquitoes are hungry, but swatting at the ones who surreptitiously draw her blood.

With mosquitoes, multispecies care involves close-up, fleshly relations. Blood is the mediating substance, either fed voluntarily as a meal sourced from blood banks or involuntarily as mosquitoes escaped from their cages bite the biologists tending to them. These hominid-insect relations are uncomfortable and ambivalent, shifting between caring with the mosquito as a public health technology and defensive care for oneself from insect bites. Yet these relations are necessary for the WMP’s intervention—with humans acting as a source of nutrition in exchange for the Wolbachia mosquito’s reproduction and protection from disease.

However, burdens of care are never equally distributed (Murphy 2015) and the experimental coexistence with mosquitoes extends beyond the insectary to draw upon the population of Medellín, who must tolerate more frequent mosquito bites during release periods and beyond. Residents’ participation in caring for these mosquitoes goes so far as to raise the insects in their backyards in Wolbicasas, little boxes containing capsules of bacteria-infected eggs that later mature into adults.

Overall, the intervention is positively received in Medellín, bolstered by the WMP’s concerted and effective social engagement in which it presents the new mosquito as a healthy ally. Yet the ambivalence of caring for such a creature is always present. After a presentation about the technology, residents would often express uncertainty concerning how to act, asking “can I kill the mosquito?” WMP fieldworkers would explain that the release of modified mosquitoes does not mean that residents have to let themselves be bitten and can continue with their preventative efforts. Instead, they emphasized that “what we are going to do is a replacement—of mosquitoes that are vectors and transmitters, for mosquitoes that carry Wolbachia,” or, as it was put more simply, “healthy” mosquitoes were replacing “bad” mosquitoes. Yet the fact that one cannot discern with the naked eye which mosquitoes are safe highlights the complexity of multispecies care in the case of a potentially disease-spreading creature.

The multispecies care involved in living with a biting insect that is simultaneously public health tool and potential threat, depending on whether or not it carries Wolbachia, is thus deeply marked by ambivalence. In fact, the multispecies care required by the WMP’s intervention cannot not be ambivalent, because of the nature of the creature involved. The underlying reality is that these “mosquitoes are going to bite you,” says WMP’s global director. The success of the intervention depends on fleshly relations, insofar as the mosquito needs human blood to reproduce. Therefore, the kinds of entanglements being created merit close attention to avoid celebrating or romanticizing violent and toxic relations (Roberts 2017). The disputed biopolitics of vector control in Medellín reflect conflicting conceptions of how to take care with/of mosquitoes. While the WMP releases mosquitoes, Medellín’s local vector control teams fumigate, leading to tensions in the management of making live and of killing, and marking distinct visions of multispecies care. Thinking care with mosquitoes highlights the challenges and ambivalences of multispecies engagements, while demanding an attentiveness to the inequalities, limits, and political stakes present in them.