The Arachnomatron

Spiders are often innocuous, mindless animals that only think about their next meal. However, despite their lack of a eusocial community that other insects have, there still exist some spiders that do take on the role that is held by queen bees and other social insects. These spider queens don't are so advanced in their commanding abilities that they don't have to be in the same colony as the lesser spiders. Spider queens have developed powerful magical abilities that allow them to give subconscious commands to their kin that would help the greater good. Although these powerful beings are extremely hidden and not well known, a select few adventurers have come across these before, and some have even agreed to a pact, that would allow the person to use the spider queen's power for the betterment of the environment, for spiders and other animals alike. 

Expanded Spell List

The spider queen lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Level 1: Entangle, Animal Friendship

Level 2: Blindness/Deafness, Web

Level 3: Slow, Nondetection

Level 4: Freedom of Movement, Phantasmal Killer

Level 5: Commune with Nature, Contagion 

Eight Legged Companion

Starting at 1st level, your patron grants you a spider that acts as your companion and link between you and the spider queen. The spider can stay in your clothes, your hair, on your shoulder, or anywhere you see fit. You gain the following benefits while the spider is within 50 feet of you:

• You can see through its eyes and hear what it hears. 
• You can speak through the spider to communicate with any other spiders that it encounters. The other spiders can't talk back, and will obey any command you give them that doesn't cause obvious harm to it.
• You gain a bonus to stealth checks equal to the spider's Dexterity bonus.
• You roll initiative for the spider and control how it acts

If the spider exists a 50 foot sphere around you, then it must succeed on a Wisdom saving throw, DC=30-Your Spell save DC, or your link to the spider will end and it will become wild. If you lose your link to the spider, or if it dies, you can be granted a new companion by your patron after a long rest.

Empowered Companion

Starting at 6th level, as an bonus action you can make your spider companion grow in size for a short time. The spider becomes a Giant Spider for 1 minute or until you choose to revert it as a bonus action. The spider has full access to the abilities of the Giant Spider, and the range that it can go to without losing your link is increased to 100 feet. If the spider exists that range, then it reverts immediately, and if it succeeds on its saving throw, it must use the Dash action on each of its turns to return to the 50 foot area. It does not have to redo its saves while it returns to you. The spider reverts to its normal form if it runs out of hp as a Giant Spider.

Once this feature is used, you can't use it again until you finish a long rest.

Fangs of the Arachnid

Starting at 10th level, you gain the ability to use the venom of your spider companion to its fullest extent. As an action on your spider companion's turn, you can choose to make it do a bite attack against an enemy that the spider crawls on. The attack is considered Finesse, and, on a hit, deals 1d4+Str/Dex and the target must succeed on a Constitution saving throw against your spell save DC or take 2d6 poison damage. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.

This attack can be used an amount of times equal to your Charisma modifier. You regain uses of this ability after a short or long rest.

Spider Lord's Venom

Starting at 14th level, your connection to your patron grows to the point where your spider companion's fangs have to ability to bring about swarms of spiders from the bodies of victims. When using your Fangs of the Arachnid ability, you can expend a spell slot to empower the venom, increasing the poison damage by 2d6 for each level spell slot expended, however the damage of the attack can't exceed 10d6. In addition, if that attack reduces a creature, that is not a construct or elemental, their corpse will turn into a swarm of spiders, using the stats of a swarm of insects, after one round has passed. When the swarm appears, it rolls its own initiative, and you control it during combat, unless it moves more than 50 feet from you, when they will disperse into the surroundings.