“The picture shows "Daphnia magna", the largest representative of the genus "Daphnia", small freshwater crustaceans (also known as water fleas), which are among the oldest model systems in biological research. Like any other organism, "D. magna" are constantly challenged by microorganisms trying to invade their body. One of these villains is "Pasteuria ramosa", a bacterial parasite castrating its host after successful establishment. The comparison of a healthy (left) and a heavily infected (right, 30 days post infection) female under a stereomicroscope reveals the consequences of parasite invasion: while the uninfected animal holds developing neonates in its brood chamber, this chamber is empty in the infected animal. Note also, that the hemolymph of the infected female is filled with "P. ramosa" endospores, the transmission stages, hence the opaque instead of translucent appearance of infected compared to healthy females. After the death of the host, these spores will be released from the carcass and consequently be ingested by new hosts, completing the horizontal transmission and starting a new life cycle of "P. ramosa".”