hive entrance, defending it from any invaders such as wasps. The number of guards varies from season to season and from species to species. Entrance size and daily traffic also play an integral role in the number of guard bees present. Guard bees of the species Tetragonisca angustula and Schwarziana quadripunctata are examples of eusocial bees that have been observed hovering at their nest entrances, providing more protection against intruders. Foraging bees (days 22–42) The forager and scout bees travel up to 3 kilometres (1.9 mi) to a nectar source, pollen source or to collect propolis. Genetic characteristics In most common bee species, worker bees are infertile due to enforced altruistic kin selection, and thus never reproduce. Workers are nevertheless considered female for anatomical and genetic reasons. Genetically, a worker bee does not differ from a queen bee and can even become a laying worker bee, but in most species will produce only male (drone) offspring. Whether a larva becomes a worker or a queen depends on the kind of food it is given after the first three days of its larval form. Gut bacteria The workers perform different behavioural tasks in the colony that cause them to be exposed to different local environments. The worker gut microbial community composition is found to be associated with the behavioural tasks they perform, therefore also with the local environment they are exposed to and the environmental landscape is shown to affect the gut microbial community (gut microbiota composition) of honey bees. Stinger The worker bee's stinger is a complex organ that allows a bee to defend itself and the hive from most mammals. Attacking bees aim for the face by sensing regions with high levels of carbon dioxide (like mosquitos). Bee stings against mammals and birds typically leave the stinger embedded in the victim due to the structure of flesh and the stinger's barbs. In this case, the venom bulb stays with the stinger and continues to pump. The bee will die after losing its stinger, as the removal of the stinger and the venom bulb damages or removes other internal organs as well. The barbs on the stinger will not catch on most animals besides mammals and birds, which means that such animals can be stung many times by the same bee. Symbolism The worker bee is a symbol of Manchester, England. It was adopted as a motif for Manchester during