Readers’ wildlife photos

Today we have a photo-and-text story from Athayde Tonhasca Júnior, a story about bees. It’s very good, so don’t pass it by, and be sure to watch the video linked near the bottom.

Athayde’s text is indented, and you can enlarge the photos by clicking on them,

Barbarians at the gate

On the morning of 24 August 410, Roman citizens awoke to another bleak day of despair, illnesses and famine. For many months they had been confined to their beloved city, under siege by some 100,000 warriors led by Alaric I, the king of the Visigoths. The invaders had blocked Rome’s 12 gates and stopped all traffic on the river Tiber, thus cutting off victualling. What have saved the Romans’ bacon so far were the mighty walls that encircled the city. But on the following evening, a dire situation turned into catastrophe when the Visigoths sneaked in through the Salarian Gate and invaded Rome. Nobody knows for sure how that happened. Some said the gate was opened by servants of a noblewoman who wanted to end the Romans’ suffering. Others suggested it was the work of slaves, who understandably held a grudge against their masters. Whatever the cause, the breach of the Salarian Gate led to three days of carnage, looting and devastation. Some historians regard the sack of Rome by Alaric’s troops as the beginning of the end for the Western Roman Empire.

Porta Salaria (Salarian Gate), by Giuseppe Vasi (1710–1782) © Wikimedia Commons:

History is not one of the favourite subjects among social bees, but one lesson from the sack of Rome by the Visigoths would resonate with them: never, ever, neglect your gates.

Only about 9% of all bee species exhibit some degree of social behaviour, from just living together to full cooperation in food gathering and care for the young. Bees’ communal living arrangements may comprise one or more queens and a few workers or thousands of individuals, as is the case of honey bees (Apis spp.). Regardless of their numbers, these bees depend on their nests for safeguarding their queens, brood and food stores. Many a predator or parasite would have a field day by sneaking in. Naturally, bees do their best to prevent that: they may sting, bite, squirt noxious chemicals, or mob a perceived intruder. Still, nests are vulnerable to a cunning burglar, particularly through openings to the outside world.

Asian hornets (Vespa velutina) storming a poorly defended entrance of a European honey bee (Apis mellifera) hive © Diéguez-Antón et al., 2024:

Social bees face a dilemma in relation to their nest fortifications. Narrow openings and those that are sporadically closed offer the best protection, but they also hinder workers’ vital comings and goings. So bees tend to follow the Goldilocks principle, balancing ease of defence and access. Indeed, for many species, foraging traffic is correlated with nest entrance size (Couvillon et al., 2008).

Nest openings of Tetragona ziegleri (a), Ptilotrigona occidentalis (b), Scaura argyrea (c), Trigonisca pipioli (d), and Trigonisca pipioli (e) © Streinzer et al., 2016:

Besides entrance size, nest architecture helps to keep enemies at bay. Some bees smear resins or wax around their doorways, putting off or entrapping ill-intentioned visitors. This tactic can be quite effective: an Amazonian Trigona stingless bee, possibly T. cilipes, builds its arboreal nest very close to an ant’s nest. As the mood of ants in general ranges from angry to enraged, T. cilipes gets free protection from their aggressive neighbours. To discourage ants from being tempted by their juicy larvae and honey, bees cover their nest with a sticky resin and build a long, waxy entrance tube. This arrangement prevents ants from invading the hive, and bees from being snatched by ants (Marconi et al., 2022).

The entrance tube of Trigona cf. cilipes can be 1.2 m long © Marconi et al., 2022:

But as design ingenuity goes, it’s hard to beat Partamona testacea, another Neotropical forest denizen. Its nest, built inside termite mounds, opens into a chamber (vestibule) crisscrossed with filaments of earth and resin. The labyrinth-like vestibule is occupied by a mass of worker bees, who, despite lacking a sting, can dispense powerful bites. This elaborate barrier makes life very hard for any pollen or nectar robber (Camargo & Pedro, 2003).

A P. testacea nest inside a termite mound. Scale bar = 5 cm © Camargo & Pedro, 2003:

Nest architecture alone may not be sufficient to deter intruders. So, most social bees, just like social wasps, post sentinel workers armed with stings or sharp teeth. If you ever found yourself too close to a bee or wasp nest, you may have a personal experience of their efficacy. The South American stingless bee Tetragonisca angustula adds another layer of security. Some guard bees stay put by the nest gates, others hover nearby. But this air force is not randomly distributed: hovering bees position themselves more or less in equal numbers to the left and right of the nest entrance, facing inwards. This configuration forms an aerial corridor through which approaching bees must pass, so any outsider will be promptly spotted and attacked by the guards. This defence strategy is important because the first arriving intruders often are scouts. If these spies are allowed to get back to their mates, a nest may soon be overwhelmed by a horde of enemies (Shackleton et al., 2018).

A: Hovering guards of T. angustula are positioned on each side of the entrance tube. B: A guard (left) fighting with a Lestrimelitta limao robber bee © Shackleton et al., 2018:

Posting guards must be energetically costly for a colony, so some bees may resort to making a run for it to avoid enemies. This is the tactic adopted by the Heller’s bee (Partamona helleri). To get home quickly and dodge predators, this bee builds a nest opening that functions as a navigation beacon. The structure is shaped like a conch shell with a lower ramp from where bees take off, and a vaulted ceiling to receive returning bees (Camargo & Pedro, 2003). This odd construction inspired the bee’s common name in Brazil: abelha boca de sapo (toad’s mouth bee).

A Heller’s stingless bee nest opening © Nelson Wisnik, BioDiversity4All:

While most bees returning home slow down for a controlled, smooth landing, Heller’s bees do the opposite. They speed up as they approach the nest entrance, colliding headfirst with the vaulted ceiling, then bouncing downward into the tunnel (Shackleton et al., 2019). Watch a worker arriving home inelegantly but safely.

You may think that bees that build nests designed for running away from danger must be defenceless: you would be wrong. Heller’s bees are bad tempered and highly aggressive, and just like honey bees, they resort to kamikaze sorties to ward off enemies. They will mob a perceived intruder, man or beast, tangling in their hair or fur while dispensing painful bites. Thanks to the Heller bee’s sharp, serrated teeth, its bite is more painful than a honey bee sting (Shackleton et al., 2015). Worse still: an attacking bee won’t let go, frequently dying while a victim struggles to dislodge it. Predators and parasites take considerable risks by raiding a seemingly vulnerable Heller’s bee nest.

A deceivingly sweet looking Heller’s bee © Carlos Alexandre Mattos Raposo, BioDiversity4All:

The examples above are a tiny sample of the myriad strategies used by bees to protect their nests from invaders. Complex, labour intensive constructions and associated types of behaviour are fine examples of natural selection at work, and certainly many more similar cases wait to be discovered.